Social and Demographic Determinants of Consanguineous Marriage: Insights from a Literature Review

Abstract

Consanguinity is the marriage of two related persons. This type of marriage is one of the main pillars when it comes to recessive hereditary diseases, birth defects, infertility, miscarriages, abortion, and infant deaths. Intermarriage continues to be a common practice in various communities in North Africa, the Middle East, and West and South Asia, as well as among migrants from Europe and North America, even though in more and more countries it has become illegal. Even if security and stability are some of the motivations for consanguineous marriage, studies show that women often suffer physical and verbal abuse from their husbands. However, because of the blood bond, tolerance for these habits is much higher. In addition, it seems that the divorce rate is much lower because separation would affect the entire state of the family. The choice of partner is significantly influenced by variables such as limited access to education and financial resources. Illiterate people coming from poor rural areas are much more likely to choose consanguineous marriage to maintain wealth in the family. The lack of medical knowledge about the negative effects of consanguinity leads to an increased rate of abortions, infant deaths, and births of children with congenital birth defects. Today, because of the process of urbanization and increased levels of knowledge, the younger generation is becoming increasingly less receptive to this particular form of marriage. In addition, as education has become more accessible to women, they have become more independent and eager to fulfill their own goals and not the wishes of the family. In conclusion, contrary to the many apparent advantages of consanguineous marriage, partners should put genetic risks first, as medical problems bring with them increased costs in the medical system and also within the family, leading to even lower economic status and consequently perpetuation of this type of marriage.

1. Introduction

Consanguinity is the marriage between two people who share an ancestor. First-degree consanguinity refers to the union between two people whose parents are siblings, while second-degree consanguinity refers to the union between two people whose grandparents were siblings. This type of marriage is one of the main pillars when it comes to hereditary recessive diseases, congenital defects, and therefore infertility, miscarriages, and infant and newborn deaths (Güler and Yavaş Çelik 2022).

In clinical genetics, a consanguineous marriage is defined as a union between persons who are related as second cousins or closer, characterized by a consanguinity coefficient (F) of 0.0156 or greater. This coefficient (F) indicates the proportion of genes at which the offspring of a consanguineous relationship are likely to receive identical alleles from both parents. The inbreeding coefficient, F, represents the probability that two genes at any locus in a person are the same through descent, i.e., have been inherited from a common relative. F has a higher value the more related the parents are. The average population inbreeding coefficient (α) is calculated according to the formula α = ∑$p_i{F}_i$, where $p_i$ is the proportion of couples in each inbreeding class $F_i$ (Jaber and Halpern 2014).

Individuals whose parents are consanguineous will have a much higher percentage of homozygous genome, and the higher the degree of relatedness between the parents, the higher the percentage of the homozygous genome. For example, the amount of genetic material shared by first cousins is four times greater than that shared by second cousins. There are four different types of marriage between first cousins.

One can talk about ‘parallel’ cousin marriage, i.e., a union between the children of two brothers or two sisters, or ‘crossed’ cousin marriage, i.e., a union between a child of a brother and a child of his sister. However, it is very important to note that the inbreeding family structure does not affect the kinship coefficient for autosomal genes, since these genes are inherited from previous generations, regardless of the sex of the individuals involved. Another type of cousin relationship is where two siblings in one family marry two siblings in another family. This relationship gives rise to the concept of ‘double first cousins’. The two children that are born will be related to each other through both parents’ families and will share the same set of grandparents, which is not the case between normal first cousins. Genetically, they have the same degree of relatedness as half-siblings. If identical twins from one family marry two siblings from another family, the children born will be even more closely related (Clarke 2019; Hamamy et al. 2011).

Reports on consanguinity rates may sometimes include marriages between third cousins or more distantly related individuals (F 0.0039). Although this discrepancy affects the total consanguinity rate, because of the lower coefficients of inbreeding in more remote unions, it does not markedly alter the mean inbreeding coefficient (Pemberton and Rosenberg 2014).

Marriage between first cousins is one of the most widespread forms, occurring in 20–30% of certain communities. These marriages are an ancient and highly respected tradition in many communities in North Africa, the Middle East, West Asia, and southern India. Consanguine unions are also common among immigrant communities practicing this custom, now living in Europe, North America, and Australia (Kumar and Chadwick 2024). Compared to regions in Asia, Africa, and the Arab world, in Western countries such as North and South America, Australia, Japan, the Iberian Peninsula, and much of Europe, the prevalence of inbreeding is low (1–10%) (Elmugadam et al. 2024).

It seems that the prevalence of this type of marriage depends on the ethnicity, religion, culture, and even the geographical area of the union members. Given that almost one billion individuals worldwide adhere to this tradition, it is evident that economic and societal reasons have undeniably contributed to its enduring existence. The presence of endogamy is thought to be greatly influenced by factors such as the age of related individuals, similar socioeconomic conditions, the physical traits of relatives, and traditions for or against inbreeding. Also, this type of union can significantly vary among some populations due to rural–urban mobility, fertility trends, the increasing proportion of women attaining higher levels of education, and, last but not least, political and civil decisions. The vast majority of studies regarding the frequency of inbreeding have detected small negative or positive changes, leading to the conclusion that this cultural trend is likely to remain stable in the future or to decline at a slow pace. For this practice to persist over time, there were, of course, some positive factors that helped to maintain it. For example, wedding preparations are much simpler, women’s autonomy is improved, marriages are much more stable, and domestic violence is less common (Kumar and Chadwick 2024).

2. Global Prevalence and Epidemiology of Consanguinity

Consanguineous marriages have been practiced since the beginning of humanity. Nowadays, approximately 20% of the world’s population live in communities that prefer consanguineous unions. The frequency of this type of marriage varies from one population to another, depending on religion, culture, and geographical area (urban/rural community). There are a significant number of countries with high levels of consanguinity in most communities, such as those in North Africa, the Middle East, West Asia, the belt that moves from Pakistan and Afghanistan in the east to Morocco in the west, and South India, where 20–50% of marriages are of this type. Additionally, in a large number of Arab countries, the rate of consanguineous marriages is very high. In many communities around the world, there is a whole tradition related to consanguineous unions, particularly in countries of the Middle East, North Africa, and South Asia (Bener and Mohammad 2017).

For example, Pakistan has one of the highest prevalences of consanguineous unions in the world, which has remained constant over time. It is a multicultural area, with various castes and different Islamic sects living in its five provinces. To date, all studies from various regions of Pakistan have shown an increased number of consanguineous marriages and their association with various acquired recessive diseases (Khan and Mazhar 2018). The highest rate of endogamous unions has been associated with low socioeconomic levels, illiteracy, and rural residence. Recent studies indicate that the prevalence of cousin marriages ranges from 51% to 58% in Jordan, from 49% to 33% in Tunisia and Morocco, and between 40% and 47% in Yemen. The prevalence is 54% in Kuwait; 58% in Saudi Arabia; 50% in the United Arab Emirates; 52% in Qatar; 50% in Oman; and 68% in Alexandria, Egypt (Bener and Mohammad 2017).

On the other hand, cases of consanguineous marriages are around 1–5% in Southern Europe, South America, and Japan, and less than 1% in Western Europe, North America, and Oceania (Soheilirad 2020). Even though the rate of consanguineous marriages in the USA is 0.1–0.2% and in Canada it is 0.3–1.5%, it is considerably higher in some isolated population groups such as the Amish. These groups do not practice unions between first cousins, but marriages between more distant cousins have been common in the past, leading to a high degree of consanguinity. Another group, the Hutterites, represents a closed community that practices marriage among relatives. They are a population in North America that surpasses the Old Order Amish in terms of cousin marriages. Due to a small number of immigrant ancestors, the strictness of endogamous marriages, and the limited size of subgroups, there is a high coefficient of consanguinity. Some studies have indicated that the husband is often much more closely related to the wife than second cousins, but not as much as first cousins. The increased frequency of consanguinity also occurs in some Native American communities, such as the Cree Indians in Saskatchewan, Canada, the Lumbee Indians in North Carolina, and groups of Americans in North, South, and Central America. In South America, the rate of endogamy is quite low, with the lowest being in Argentina (0.29%) and the highest in Venezuela (1.84%) (Jaber and Halpern 2014; Hamamy and Alwan 2016). In Norway, the proportion of Pakistani-origin women married to a relative has decreased from 45.5% in 1995–1997 to 27.3% in 2002–2005 for those born in Pakistan and from 48.3% to 18.8% for those of the same origin but born in Norway. The changing immigrant culture, along with the gradual shift from traditional consanguineous unions to those preferred by the dominant society in the country they live in, could be an explanation for the decrease in the frequency of cousin marriages (Jaber and Halpern 2014; Hamamy and Alwan 2016; Oniya et al. 2019). However, this is not always the case. For example, according to a study of a sample of people of Pakistani origin in the United Kingdom carried out in Oxford and West Yorkshire, the rate of marriage between first cousins has increased substantially among the younger generation compared to those in the past. This increase shows that it is not just a desire to follow cultural preferences, but that some parents simply believe it is right to take into account the obligation to consider the fact that their grandchildren could be future spouses for their own children. For people living in the same country, marriage preferences persist when they move from a less developed area to a more developed region, but their frequency depends on the time spent in the new place. For example, in a suburb of Izmir, Turkey, consanguineous marriages are 4.7 times more common among women who have moved in the past 10 years compared to those who have lived in the area for more than 10 years (Kumar and Chadwick 2024).

Jews and Buddhists forbid consanguinity, while Islam favors such unions. Additionally, while Christianity once tolerated consanguineous marriages, it now prohibits them. Marriage rates have increased or remained unchanged in the oil-rich Middle East due to the belief that it preserves family wealth. In smaller immigrant communities, this practice plays a crucial role in preserving moral, social, and religious norms. Nowadays, the disadvantages of consanguineous unions are considered much smaller compared to the past. However, particularly in Western communities, consanguinity carries a certain social stigma. Moreover, with the increase in education levels, the fact that such marriages can result in children with congenital malformations has become more widely known among the general population. This awareness has contributed over time to the decrease in the number of endogamous marriages. Additionally, education—particularly among women—has changed the age at which they marry, leading to a preference for marrying at an older age. For instance, uncle–niece unions have been prohibited among Punjabi Muslims in India, resulting in a general decrease in consanguinity. In other countries, such as the U.S., marriage between cousins is prohibited in most states and can only be performed with a special license within a few small immigrant groups under certain circumstances (Kumar and Chadwick 2024; Oniya et al. 2019).

3. Why Is Consanguinity Respected and Preferred in Some Populations?

Consanguinity has had support throughout history and continues to be popular in some communities even today. One explanation for this is that people are still influenced by culture and religion. The question that arises is why this practice is still present even though the cultural and religious aspects have changed over time and why people still favor it, because there are studies that show an increase in birth defects among children who come from this type of union (Kumar and Chadwick 2024).

Most major religions tolerate consanguineous unions, with the exception of the Orthodox Church, a branch of the Christian faith, and the Roman Catholic Church. However, there are some exceptions; for example, the Coptic Church, which has separated from the other branches of the Orthodox Church, allows marriage between first cousins, which is also accepted by Protestant Christians, who follow the Jewish guidelines on marriage (Shaw and Raz 2015).

The Muslim religion permits marriage between first cousins, but not between uncle and niece or aunt and nephew. The Koran, Sura 004, Al-Nisa, verse 023, talks about permissible and forbidden unions: “Forbidden to you (for marriage) are: your mother, daughter, sisters, aunt, niece, step-mother, step-sister, mother-in-law, step-daughter…” (Jaber and Halpern 2014). However, even though consanguineous marriage is avoided in these areas, consanguineous unions are allowed within Sikh communities in Pakistan between first cousins of the Sikh religion (Shaw and Raz 2015). In the Jewish religion, first cousins and uncle–niece marriages are allowed, but nephew–aunt marriages are forbidden. The Book of Leviticus describes in detail the relationships that are forbidden and their nature: father, mother, half-sister, nephew, and aunt. In contrast, there is no information about relationships with a daughter or sister, but according to the teachings of the Talmud, even if these types of relationships are not mentioned, they are also forbidden (Jaber and Halpern 2014). Hindus have different rules about this type of union depending on the groups in which they live. Aryan Hindus in North India do not agree to such unions between blood relatives for seven generations on the male side and five generations on the female side. Dravidian Hindus in South India, on the other hand, agree and even support first-cousin marriages. Also, especially in the states of Andhra Pradesh, Karnataka, and Tamil Nadu, unions between uncle and niece are common. Cousin marriages were recognized in the Hindu Marriage Act of 1955, but this act prohibited marriage between an uncle and a niece. But later in 1984, through the Hindu Code Act, they also became legal (Jaber and Halpern 2014; Oniya et al. 2019).

It is believed that consanguine marriage strengthens inter-familial relationships, allows for better knowledge of the partner’s economic and health issues, and simplifies premarital cultural negotiations. For example, economics-related reasons are those related to a lower requirement for a dowry and keeping land and wealth within the family (Hamamy et al. 2011; Bittles 2008). Another reason would be that this type of marriage can significantly reduce the costs of searching for a suitable partner, and the parents of both partners know each other; therefore, the uncertainty regarding compatibility between the spouses and their families will be reduced (Kumar and Chadwick 2024).

As an example, out of a sample of 400 Muslim women in Nepal, 40.8% stated culture or tradition as the main reason for consanguinity, 26% financial burden, 11.5% family pressure, 10% ease of finding a partner, and a smaller percentage stated a lack of education as the main reason (Bhatta and Haque 2014). Women in Bangladesh reported that marrying their cousins improved their relationship with their in-laws and reduced their premarital payments. Similarly, men reported that marriage to their cousin improved their husband–wife relationship, allowed the partner to remain close to the family, and avoided division of inherited property (Kumar and Chadwick 2024).

In Karachi, Pakistan’s largest city, consanguineous marriages have previously been preferred in all ethnic and religious groups. Even nowadays, parents continue to be a prime factor in deciding on the choice of partners for sons and daughters. The most important reasons for preferring consanguine marriages are sociocultural rather than economic. Among Muslims, respect for religious traditions is the least common reason for this type of marriage. The fact that they stay within the family is something they pride themselves on, as it gives them a better social position than those who opt for exogamous marriage.

Among Pakistani communities in the UK, the advantages of marrying within the family include strengthening family ties, some economic opportunities for family members, ease of finding a suitable partner, and increased durability of the marriage. In many cases, respecting the tradition of marrying a cousin demonstrates respect for the wishes of older relatives (Kumar and Chadwick 2024). For example, in a slum from a metropolitan area of Izmir, Turkey, the deciding factor for consanguineal marriage is family in 41.2% of cases. The main perceived advantage is the fact that the partners already know each other (14.2%), and other reasons are good understanding within the couple (5.6%) and strengthening inter-family ties (3.4%) (Çiçeklioğlu et al. 2013).

4. Does Consanguinity Reduce Domestic Violence?

The World Health Organization defines intimate partner violence as “conduct occurring within an intimate relationship that causes physical, sexual or psychological harm, including sexual coercion, physical assault, psychological abuse.” Domestic violence is endemic globally and adversely affects the health and economic well-being of women and society as a whole (World Health Organization 2010). In a study of 400 women aged 15–49 years in Nepal, about 2/3 reported having been assaulted in marriage, but it was concluded that domestic violence is less common among consanguineous marriages than in ordinary marriages (Kumar and Chadwick 2024). Another study was carried out in the city of Rawalpindi, Pakistan, to determine whether there is an association between domestic violence and cousin marriage, using a standardized and validated assessment modality called the “Abused Women’s Screening Tool”. A total of 1010 married women were interviewed during this study, 484 consanguineous and 526 non-consanguineous. Of all types, emotional abuse was the most common (71.4%), followed by sexual abuse (52.2%) and physical abuse (50.6%). Therefore, marriage to one’s own cousin is not a protective factor against emotional abuse, but physical and sexual abuse are less common in consanguineous families. Furthermore, 17.3% of women from non-consanguineous families reported frequent physical abuse, compared to 13.8% from consanguineous families. Regarding sexual and emotional abuse, 22.4% and 26.2% of women with non-related husbands reported being frequently abused, compared to 17.1% and 22.3% in the case of those with related husbands. Many of the women who were not married to a relative reported feeling more often frightened by what their husband does or says than those in consanguineous families. Knowing the husband first as a cousin, before being their partner, makes women feel less frightened or not frightened at all, even if sometimes abuse is present (Shaikh et al. 2014).

In Egypt, an interview study involving 5606 women concluded that 24.3% were part of a consanguineous marriage. A study found that 31% of those married to a paternal cousin, 34.9% of those married to a maternal cousin, and 36.2% of those not from a consanguineous family were physically assaulted. Domestic violence among these women was lower if the husband was a first or second cousin, especially a paternal cousin, than among those married to a more distant relative or stranger (El-Zanaty 2006).

Unfortunately, several testimonies from around the world suggest that quite large numbers of women are subjected to domestic violence during pregnancy. For example, a survey of a sample of 517 women in Jordan was conducted to estimate the prevalence of physical violence against women during pregnancy and to examine the risk and protective factors associated with its occurrence. Of these, 46% were from consanguineous families and 54.1% were from unrelated marriages; therefore, marrying a stranger increases the risk of domestic violence. Other studies have also concluded that forgiveness is more common in consanguineous couples because kinship ties to the spouse’s family lead to an underestimation of the offense suffered by the victim (Clark et al. 2009).

5. The Influence of Consanguinity on Divorce

Although comparative data on the stability of consanguineous versus unrelated marriages are limited, the available evidence suggests that divorce is less common among consanguineous couples, mainly because divorce would be disruptive for the whole family. A study in Iran that investigated 496 couples who were planning to divorce and 800 who were not concluded that marriage survival was significantly lower for unrelated than for related partners. Similarly, a report from Sudan indicated greater marital stability in consanguineous unions, regardless of the type of kinship relationship. Also, of the families selected in the Oman National Health Survey, consanguineous marriages were more stable than ordinary marriages (Kumar and Chadwick 2024).

Two other studies, one that included participants from Pakistan and one from Sudan, found that this type of marriage is preferred because women feel that they are better treated by their husbands, have security, and have a stable and long-lasting marriage. Furthermore, 96.7% of the women who were part of a consecrated marriage included in the Pakistan study said they would make the same choice for their daughters (Elmugadam et al. 2024; Khan and Mazhar 2018). It appears that, compared to marriages between unrelated persons, the risk of divorce is lower in consanguineous families (Elmugadam et al. 2024). The stability of this particular marriage is seemingly attributed to their adherence to family culture and customs, their level of social compatibility, and their ability to seamlessly assimilate into the new family (Hajjaji et al. 2024).

6. Consanguinity and Educational Status

Several studies have shown that the rate of consanguineous marriages, especially in consanguineous populations, is influenced by the educational level of both women and men. For example, in Nepal, consanguineous marriages account for 36.7%, and this higher rate is associated with higher levels of education among men. Consanguineous marriages are 3.35 times more common when spouses have higher education compared to those who are not even literate (Bhatta and Haque 2014).

Within the Bedouin population in Israel, where 44.8% of marriages are consanguineous, there is a notable correlation between consanguinity and husbands having more years of education compared to their wives. Educated men may be considered an asset to the family because they earn more money and can therefore financially support an extended family and accumulate more property. So, the commitment to marry a relative is higher because this is the only way to keep wealth in the family (Na’amnih et al. 2014).

Similarly, in the Arab population in Israel, based on information collected from 6437 couples, it was concluded that there is a striking association between consanguinity and the years of education of the man (Kumar and Chadwick 2024). Using the data from 4667 women included in the Iran Fertility Study (1976–1977), the incidence of inbreeding is approximately the same for all three levels of the husband’s education, contrasting with the wife’s education, for which higher status leads to lower rates of inbreeding. In other studies, among women in Iran, it was found that higher educational attainment of women leads to a lower probability of them choosing a consanguineous marriage. Similarly, in India, the chance that a woman will not choose a relative for marriage has increased with progress in female education (Kumar and Chadwick 2024).

On the other hand, this is not true everywhere in the world. An interesting finding was seen in a study focusing on Bedouins in the Beqaa Valley in Lebanon, where it was found that there is an inverse relationship between literacy and instances of consanguineous marriage. Apparently, 57.78% of women who were not highly educated were married to strangers, and of those who were married to first cousins, 28.57% had elementary education compared to 17.78% among those who were not related to their husbands (Mansour et al. 2014).

Nadia Agha mentions in her 2016 article that when interviewing women in rural Pakistan, she found that most of them were illiterate or had only a few years of schooling. Those who were already in school when they married were forced to drop out of education, contrary to their wishes, because a high level of knowledge and education brings with it a low number of consanguineous marriages. In addition, girls were discouraged from going to school because during the time devoted to education, they had to learn from their mothers to be good wives. Moreover, the number of children born out of such marriages is quite high, and young wives do not have time to take care of anything other than their families. Apart from parents who oppose educating their daughters, once married, their husbands—who are often even less interested in this subject—sometimes forbid their wives from going to school, arguing that once educated, they may become less tolerant and obedient in marriage and might even refuse to marry an illiterate man (Agha 2016).

In Turkey, with the new educational reform, fewer and fewer women are choosing to marry their relatives. Firstly, they are more likely to find a partner from outside their home community, thus avoiding family-arranged marriages. Secondly, with women’s emancipation, they no longer put the family’s wishes first but their own desires and ambitions. In addition, having access to more information, they realize the negative medical effects of inbreeding. On the other hand, it seems that men do not share the same point of view as women (Akyol and Mocan 2023).

Among the population living in the occupied Palestinian territory (oPt), according to a cross-sectional study in 2022, it was observed that the highest number of consanguineous marriages was reported among couples who had parents with very low educational levels. An increased level of education is associated with decreased consanguinity, as today’s young people are more medically informed and are no longer willing to take the risks of a consanguineous marriage (Ghanim et al. 2023).

Also, in a 2018 cross-sectional study that took place in Sudan to assess awareness of the health impacts of consanguinity, the same close link between education level and consanguinity was found. The highest percentage of consanguineous marriages was found among participants with no formal education (60.8%), and the lowest percentage was found among those with university and postgraduate education (24.3%).

Two other studies from Pakistan have emphasized that with the educational development of young people and the consequent increased accessibility to information on medical genetics, curiosity about the medical challenges of consanguine marriage has increased. Couples are increasingly interested in preconception counseling, regardless of the influence of religion and sociocultural background. Thus, it appears that a lower rate of education among women and a higher rate among men lead to a higher percentage of unions between relatives, whereas a much higher level of education among women causes this percentage to be decreased (Khan and Mazhar 2018; Malik et al. 2024).

7. Age at Marriage and Fertility Rates in Consanguineous Marriages

In many studies on the association between consanguinity and age at marriage, it has been found that women married to a first cousin are often much younger than those married to an unrelated person. One reason suggested for marrying at an early age is economic, as the marriage of a very young daughter leads to a secondary income for her family. When an educated woman can contribute to the family income, there is no financial advantage for the household when the woman marries early. Moreover, working women find it much easier to marry unrelated husbands because they are more visible in society (Kumar and Chadwick 2024). Besides the ages of the couples in these marriages, the age of the parents who establish the event also plays a role. Most often, consanguineous couples come from poor, low-educated families who had arranged marriages at an early age and consider this to be the right choice for their offspring (Elmugadam et al. 2024).

Among Bedouin women in Israel, there was a significant association between consanguinity and women’s young age at marriage. A similar finding was also reported in Yemen and Oman (Kumar and Chadwick 2024). On a similar note, among the Arab population in Israel, a study that included 6437 couples concluded that women in consanguineous marriages tended to marry at a younger age than those with unrelated partners (Na’amnih et al. 2014). Likewise, among 141,000 couples residing in the Gaza Strip (part of the occupied Palestinian territory), the average age of individuals married to first cousins was significantly lower (22.4 ± 5 years) compared to those married to second cousins (24.3 ± 6 years) and to unrelated individuals (26.5 ± 8 years) (Sirdah 2014). A study conducted among the population living in the occupied Palestinian territory (oPt) found that in both 1995 and 2004, over 70% of individuals who married after the age of 25 opted for a spouse who was not related to them. Also, in South India, data indicates that a woman who marries at an older age is much more likely to choose a non-blood relative than one who marries early. This habit of women marrying a cousin at an early age has also been detected among immigrant populations (Assaf and Khawaja 2009; Audinarayana and Krishnamoorthy 2000). For example, in a retrospective analysis of 1964 consultations at the Outpatient Clinic for Prenatal Genetic Counseling at the Medical University of Vienna, 8.9% of all patients were part of a consanguineous union. The patients who were consanguineous were notably younger, and most of them had relatives who were not of Austrian descent (Posch et al. 2012).

Even though the age of marriage for women in Pakistan is 16, this rule was completely ignored in the villages of Khairpur, where N. Agha interviewed several women in 2016. She found that the average age at marriage for women was 15, with some of them stating that when they got married, they were 11–12 years old. In rural areas, plans for a future marriage begin as soon as the girl has her first menstruation, with age not being an important criterion for parents, but rather the ability to procreate. Out of a total of 30 women N. Agha spoke to, 12 said they were 11–14 years old when they got married (Agha 2016).

Moreover, studies have shown that consanguineous families tend to have more children than families with unrelated partners. One possible explanation for this phenomenon is that offspring born to closely related parents are more likely to experience infant mortality. As a result, these individuals may exhibit higher fertility rates in an attempt to counterbalance this detrimental factor (Kumar and Chadwick 2024). Another explanation could be the longer reproductive period for inbreeding couples because they choose a younger age for marriage. Some studies have also shown that contraceptive measures are used much less when partners are related (Cheffi et al. 2022).

Multiple studies indicate that couples who are closely related by blood have a better likelihood of experiencing a higher number of pregnancies, live births, and surviving offspring. This is because consanguineous parents tend to have a younger average age, which increases the chances of early fertility initiation (Kumar and Chadwick 2024). At the molecular level, it is thought that the long-term practice of inbreeding may eliminate harmful recessive genes from the population over successive generations through the death of affected individuals. In addition, compelling data indicate that families with a history of inbreeding tend to have children up to older ages, therefore prolonging their reproductive span (Ghanim et al. 2023; Rao and Inbaraj 1979; Nuhii et al. 2022).

On the other hand, studies show that the number of stillbirths, miscarriages, problem pregnancies, and children with various pathologies has increased as a result of inbreeding. In addition to the risks to the fetus’ health, pregnancy within a consanguineous marriage can have significant consequences for maternal health. Women in such marriages face an increased risk of obstetric complications, such as preeclampsia, antepartum or postpartum hemorrhages, and premature birth, partly due to common genetic predispositions for autoimmune or metabolic disorders. Additionally, the incidence of recurrent spontaneous abortions is higher due to the accumulation of homozygous recessive mutations that lead to defective embryogenesis. In addition, severe fetal malformations associated with consanguinity increase the frequency of therapeutic pregnancy terminations, induce complicated labor, and increase the need for emergency surgical interventions. In addition to the risks associated with surgical interventions caused by miscarriages, the psychological impact is quite significant, as women may suffer from depression and anxiety after losing a child. Some studies from regions where consanguinity is a traditional practice have highlighted an increased maternal mortality rate against the backdrop of perinatal complications and inadequate medical access. In general, women in these communities are also exposed to an additional risk due to cultural pressure to have multiple pregnancies, which can lead to physical exhaustion, severe anemia, and cumulative complications. Moreover, despite the increased accessibility of medical services, socioeconomic differences still result in inequity among patients. Reducing these risks involves implementing effective genetic counseling programs, rigorous prenatal monitoring, and reproductive education (Güler and Yavaş Çelik 2022; Sevinç and Çelik 2016).

Currently, young people hold an unfavorable view of consanguinity, resulting in a decline in the prevalence of consanguineous marriages. This shift can be attributed to their heightened awareness of the medical hazards associated with such unions, which has been facilitated by education (Ghanim et al. 2023).

8. Socioeconomic Status and Inbreeding

Some of the economic factors that lead certain populations to choose consanguine marriage are the retention of family property among the wealthy and the reduction in the value of dowries among poorer families. A dowry is the major economic transaction underlying the marriage decision (Elmugadam et al. 2024). In Arab countries, a dowry in the form of money or jewelry is sent to the bride on behalf of the groom. In contrast, in Southeast Asia, the dowry (in the form of land, vehicles, gold, money) is given from the bride to the groom. Wedding negotiations are simpler in a marriage within the family, and the value of the dowry is usually lower. In the case of consanguineous marriages in Pakistan, the demands from relatives for the wedding gift are lower, and the desired value is more affordable. The bride and her family are much less likely to be ‘penalized’ for any shortcomings that arise in the gift given before the wedding (Khan and Mazhar 2018; Hussain 1999).

In Bangladesh, if the parents of the bride who is marrying a relative are unable to provide the dowry before the wedding, it will either be decreased in amount or its payment will be postponed. It also seems that such payments can be reduced by 25% in the case of a consanguine marriage compared to a normal marriage. Also, in Bangladesh, because the dowry is given by the bride’s family to the groom, the choice of marriage to her cousin is affected by her family’s wealth more than that of the groom. Among 52,000 marriage decisions between 1982 and 1996, changes were observed in the choices of rich versus poor households. For example, brides from riverside but flood-protected households in this region chose grooms from wealthier families, and few of them chose relatives as their partners, compared to those living in the flood-prone area, who made no such claims. It can therefore be seen that the mere presence of a dike freed the brides from the obligation of consanguine marriage, unlike the poorer ones, without the possibility of freeing themselves from this tradition (Mobarak et al. 2013).

Another example may be observed among the population living in the occupied Palestinian territory (oPt), where the increasingly severe economic circumstances contribute to an elevating prevalence of consanguinity. This is because a familial union not only involves a reduced dowry but also offers the advantage of preserving wealth and land within the family. Moreover, it appears that the wealth index is significantly influenced by consanguine marriages. Hence, it appears that cultural, social, and economic factors collectively impact marriage choices in populations where consanguinity is a prevalent tradition (Kumar and Chadwick 2024).

One of the main factors that determines marriage for economic reasons is the low level of education among women. Due to the lack of education and therefore of a job, they cannot afford to support themselves and are thus forced to respect the family’s choice of a future partner (Güler and Yavaş Çelik 2022; Akkaş and Uyanık 2016).

In a recent study that included participants from Qatar, it was shown that there is a positive correlation between higher monthly family income and the desire for consanguinity. This is attributed to the lower expenses associated with wedding preparations, which allows families to maintain their wealth within the family (Abdu et al. 2023). Moreover, a 2022 study emphasizes that people with a low income avoid this type of marriage due to medical repercussions (Ghanim et al. 2023).

Studies based on the social aspects of consanguinity indicate that this type of union is most common among people with low socioeconomic status. In the occupied Palestinian territory, the rate of consanguinity is undergoing negative changes due to the increasing socioeconomic status among women, and it seems that the frequency of consanguinity remains unchanged only in families with lower living standards. Similarly, among Bedouin women from Israel, there is a striking association between consanguinity and the low monthly income of their family. The same situation can be seen in India, where the group with the lowest socioeconomic status has the highest level of consanguinity (Kumar and Chadwick 2024).

In contrast, in Turkey, the prevalence of familial relationships has decreased, especially among individuals with lower socioeconomic status. A study in Tabriz (Iran) pointed out that if the father or father-in-law has a low salary, the rate of inbreeding is much higher. As an example, in the past, men whose fathers were unemployed were about five times more likely to start a family with a relative (Heidari et al. 2014). On the other hand, in Tehran (Iran), the socioeconomic level does not seem to have significantly influenced the choice of a life partner (Akrami et al. 2009). In contrast to other regions, Yazd province has a high level of development and a high frequency of consanguinity. This is due to the conservative nature of the province, often referred to as the “house of prayer.” Women here prioritize traditional family values and fertility (Abbasi-Shavazi et al. 2008).

But even though social status seems to influence the practice of consanguine marriages, this is not generally true, as other factors such as religion, culture, and ethnicity play a role in deciding on a future life partner (Kumar and Chadwick 2024).

9. The Influence of Ethnicity and Rural–Urban Environment on Consanguinity

Ethnicity and place of residence are thought to be factors influencing the frequency of consanguineous marriages, which has been observed in studies of consanguineous populations. In general, women born in rural areas are more likely to marry a relative, whereas this is not necessarily the case for men. In Morocco, for example, the rate of consanguinity is lower in areas close to a city than in villages, and in cities, the rate of consanguinity is starting to fall more and more (Cheffi et al. 2022). In Algeria, cousin marriage is present at a rate of 10% in urban areas and 15% in rural areas; this rate is lower than that of Egypt (8.3% versus 17.2%) and Jordan (29.8% versus 37.9%), respectively. The average inbreeding rate in Syria was also found to be lower in urban than in rural areas (Kumar and Chadwick 2024). Recently, in Algeria, the rate of consanguinity reached 55.06%, and in Egypt, it rose from 17.7% to 59.9%. Similarly, in Pakistan, the rate of marriage between relatives has reached 73%, and in the Middle East and South Asia, it has increased from 45.7% to 61% in Oman. In Turkey, the percentage of inter-relative marriages was found to range from 6.4% to 44.8%, and in Sri Lanka, it ranged from 3.8% to 22.4% (Cheffi et al. 2022).

A study among women from Iran found that the rate of inbreeding was higher among rural couples. Similarly, an association between place of residence and consanguinity was found in the Beqaa region of Lebanon. In addition, in the Palestinian territories, a survey from 1995 and another from 2004 among several women indicated that the rate of consanguinity was higher for women in the Gaza Strip compared to those in the West Bank, as well as for those living in rural areas compared to those in urban areas. In 2003, a demographic survey was conducted in Turkey on consanguineous unions among a sample of married women. According to this survey, the frequency of consanguineous marriages was determined by the ethnicity of the spouses. Where both spouses were Kurdish, the level of consanguinity was higher (45%) compared to couples where both spouses were Turkish (18%). Regional disparities were seen in the prevalence of consanguineous marriages, with a rate of 10% in West Marmara and 42% in East Anatolia, which is the least developed region of the country (Kumar and Chadwick 2024).

In 2013, a cross-sectional survey of 4913 women between the ages of 15 and 65 found that 18.5% of them were in a consanguineous relationship, and 57.8% of them had their first cousin as their husband. Analyzing place of origin, 69.0% of those who had their first cousin as their husband were from rural areas, and 71.6% of those who were married to more distant relatives were from rural areas (Kaplan et al. 2016).

According to the Pakistan Demographic and Health Survey (2012–2013), consanguineous marriages were more prevalent in rural areas (54%) compared to urban areas (38%). The primary factor is that education and living standards in rural areas are significantly lower and individuals adhere to traditional ways of life. A significant proportion of Pakistan’s population resides in rural areas and faces economic hardship, relying on agriculture as their primary means of sustenance, thereby limiting their freedom. In these regions, women are seen as possessions of men, occupying the lowest position in the social order, and their lives are subject to male domination (National Institute of Population Studies (NIPS) and ICF International 2013).

Even though the number of people living in urban areas is on the rise, people migrating from rural areas may maintain the tradition of consanguine weddings because of the social, economic, and cultural benefits (Islam 2021).

10. Consanguinity and Its Implications for Health Status

A phenotype is the combination of morphological, physiological, biochemical, mental, and behavioral characteristics that biologically define an individual. Both hereditary and environmental factors influence it. The genotype is the system of genes in an individual’s diploid set of chromosomes that determines the formation of a particular phenotype. The genotype contributes to the formation of an individual’s traits. If the genotype contributes more than 50% to the formation of certain traits, these are called heritable traits. They can have monogenic or polygenic determinism. A gene is a chromosomal segment that controls the phenotypic expression of a trait, or it can also be defined as a polynucleotide segment of the DNA molecule that encodes the synthesis of a specific molecule. We can divide phenotype and genes into two categories: allelic genes and non-allelic genes (Costanzo et al. 2019).

Allele genes are located at identical loci on homologous chromosomes and control the same trait or alternative forms of the same trait. Allele genes have several molecular forms—they are polyallelic—but only two alleles are present in a person’s genotype. About 30,000 pairs of allele genes correspond to each person. If the individual carries identical allele genes, they are homozygous; if the individual carries different alleles, they are heterozygous. Another variant is the hemizygous condition, which refers to genes linked to the X chromosome in males. In heterozygosity, there is one allele with a higher activity than the other allele, and this is called a dominant or recessive gene. Genes that are not alleles are located at different loci of the chromosomes and usually control different traits or cooperate to form a complex trait. They manifest phenotypically independently of each other or interact depending on the effect of gene position within a haplotype, epistasis, or additive polygenesis (Woodward et al. 2022).

A mutation is an alteration in the DNA sequence. When mutations occur in cells that produce gametes, they can be passed on to future generations. Missense mutations result in the substitution of a single amino acid in the polypeptide chain, such as in the case of sickle cell disease, which is caused by a mutation that causes valine to replace glutamic acid at the sixth position of the beta-chain of globin. Nonsense mutations produce a stop codon and cause premature termination of translation, resulting in an incomplete protein. Mutations can occur in the promoter and other regulatory regions or in genes for transcription factors that bind to these regions. The result is either a decrease or an increase in the amount of gene product that the cell forms. Mutations differ in their effects on the phenotype, with mutations that cause a protein product to be missing or to be less active and mutations that produce a protein product that will have a new function or a much higher activity than normal (Turco et al. 2019). Consanguineous partners share a common ancestor, and because of this link, both inherited alleles are identical at some loci. Because of this common inheritance, there is a risk of increased cases of autosomal recessive disorders; the risk for congenital malformations in children from consanguineous families is 2–2.5 times higher than in the general population. Inbreeding also has a direct impact on recessive disorders by ‘producing’ homozygous recessive alleles previously ‘hidden’ in the genome of heterozygous carriers. Furthermore, inbreeding may reveal the presence of a mutation that is not lethal prenatally but could be responsible for a larger number of inherited autosomal recessive genetic disorders (Dahdouh et al. 2016; Klug et al. 2006). Some studies have estimated that the frequency of these diseases is variable, related to the age of the mutations involved and the selective phenotype pressure. In populations with a large number of inbreeding unions, the diagnosis of a new recessive disorder in a family member demonstrates a recessive mutation, whereas the presence of a rare disease in families from the same region indicates that the disease is older (Zlotogora et al. 2006; Zlotogora 2002).

Carrier screening tests are extremely valuable in determining reproductive risks and in developing medical programs to help avoid them. These tests should be carried out for the general population (couples with no genetic or family history of disease who wish to know preconceptionally the risk of conceiving a child with a recessively inherited disease); consanguineous couples who have an increased risk of recessively inherited disease in their offspring; people of ethnic backgrounds in populations where some recessive diseases are more prevalent; couples who will undergo assisted reproduction treatment as an adjunct to other diagnostic tests; and sperm/egg donors, for better selection and to reduce the risk of transmission of recessive diseases (NGS Carrier Screening Panel 2025). Usually, screening tests are used to identify asymptomatic patients in a population, such as Pap smears or travel questionnaires used during pandemics/epidemics. In terms of genetics, carrier screening attempts to determine, among asymptomatic patients, those who can pass on the altered gene or genetic risk to future generations (Gregg 2018).

Studies indicate that, on average, 2 in 100 couples in the general population are at risk of having a child with a recessive disorder. Because of the expression of autosomal recessive gene mutations inherited from a common ancestor, inbred couples are at an even higher risk than the general population of having a child with a health problem. And the closer the biological relationship, the higher the risk. Until recently, most consanguineous couples did not seek genetic counseling until a month after the birth of their child, but lately, more and more consanguineous couples are agreeing to be screened for carrier status to find out the risks of having a baby with health problems (van der Hout et al. 2023; Ricca et al. 2024; Jameel et al. 2024).

A whole-exome sequencing (WES)-based Expanded Carrier Screening (ECS) test was recently developed, validated, and diagnostically deployed for consanguineous couples at Maastricht University Medical Center (MUMC+), Netherlands. This test diverges from the European Society of Human Genetics (ESHG) recommendations to restrict the scope of ECS to severe congenital or childhood-onset disorders, encompassing a substantial array of approximately 2000 autosomal recessive disease-related genes, including relatively mild and late-onset conditions. A recent publication regarding the rate of WES-based ECS at MUMC+ indicated that 28% of examined consanguineous couples carried pathogenic variants that were previously unidentified, the majority of which were linked to severe diseases, adversely affecting quality of life, causing impairment, and/or necessitating interventions, with onset typically occurring in infancy or early childhood (van der Hout et al. 2023). Depending on the test results, couples at high reproductive risk may consider other reproductive options such as in vitro fertilization, adoption, using a semen donor, or even abandoning the idea of having a child. In addition to the preconception screening options, prenatal screening affords parents the possibility to request therapeutic procedures immediately after birth to improve the health of their offspring in case they inherit a recessive disorder (van der Hout et al. 2023; Ricca et al. 2024; Jameel et al. 2024).

Non-invasive prenatal testing (NIPT/NIPD), based on the analysis of circulating free fetal DNA (cfDNA) in maternal plasma, has undergone significant development in the past decade. While NIPT is primarily used for detecting major chromosomal abnormalities, non-invasive prenatal diagnosis (NIPD) used for monogenic diseases remains much more complex and is only available in specialized centers in a few countries. Until recently, the use of NIPD in consanguineous couples was considered difficult because the high degree of genomic homology between parents hindered the clear identification of the informative haplotypes necessary for analysis. A significant innovation, however, was brought about by researchers from the United Kingdom and Switzerland, who clinically validated a method that can be used to extend NIPD for consanguineous families by using a type of nucleotide polymorphism called “type 5 SNPs”—characterized by both parents being heterozygous. These markers, previously considered uninformative, were integrated into an adapted version of the SPRT sequential probabilistic test, thus allowing for the determination of the fetal genotype even in the absence of classic informative SNPs. This method allows for distinguishing between an affected fetus, carrier fetus, and healthy fetus by analyzing the imbalance between the inherited haplotypes (Hap1 and Hap2), even when the fetal DNA fraction is low. Adapting the SPRT method to include type 5 SNPs represents a major advancement in expanding access to NIPD for consanguineous couples, especially in cases of monogenic diseases with common familial mutations. This evolution paves the way for more personalized and inclusive reproductive medicine, with the potential to become the future standard in non-invasive prenatal diagnosis (Sistermans 2024).

One of the populations where genetic disorders are commonly found is the Jewish population. For this reason, as a preventive method, especially among Ashkenazi Jews, carrier screening has been implemented, followed by the expansion of screening panels, thus identifying disease-causing mutations. Prenatal carrier screening for recessive genetic diseases in the Ashkenazi Jewish population began with Tay–Sachs disease in the early 1970s. Since then, the number of disorders included in the screening panels has increased as causal genes and founder mutations for additional diseases have made carrier DNA testing feasible. Genetic counseling and carrier screening have been widely accepted by the Ashkenazi community, and in 2004, the American College of Obstetricians and Gynecologists updated its recommended screening panel to include four other highly prevalent neurodegenerative and debilitating disorders: Canavan disease, cystic fibrosis, familial dysautonomia, and Tay–Sachs disease. After these changes, the Medical Genetics College recommended screening for five other conditions: Bloom syndrome, Fanconi anemia group C, Gaucher disease, mucolipidosis type IV, and Niemann–Pick disease types (Scott et al. 2010; Boston Medical 2025).

In addition to screening for these diseases, many laboratories test patients for maple syrup urine disease and type Ia glycogen storage disease. Researchers have also described mutations for lipoamide dehydrogenase deficiency, familial hyperinsulinism, nemaline myopathy, and Usher syndrome types I and II in this population. Today, there are various screening programs for the Jewish population. One such program is being carried out at the Boston Medical Center, which is launching a genetic disease screening program for this population. In addition to the aforementioned diseases, this program also includes Walker–Warburg syndrome, spinal muscular atrophy, and Jaubert syndrome. The entire program consists of carrier screening, personalized risk assessment, and discussing reproductive options for couples carrying affected genes (Hamamy and Alwan 2016).

11. Conclusions

In conclusion, even if consanguineous marriage provides greater stability and a sense of protection for partners, these aspects should be weighed against the genetic risk of a congenital abnormality in their offspring. Studies based on the correlation between socioeconomic factors and consanguinity in some populations have listed a number of advantages that may encourage new generations to choose to start a family with a blood relative.

Place of origin, socioeconomic status, civil unrest, education levels, workplace, religion, and culture are among the issues that need to be considered when seeking to understand and research the factors influencing decisions in inbreeding populations. Today, this type of union is still favored and respected in many countries in North Africa, the Middle East, and West and South Asia, as well as among migrants from Europe and North America, even though in more and more countries it has become illegal (Hamamy and Alwan 2016).

Enhancing the well-being of partners in consanguineous unions requires a thorough and culturally appropriate strategy. Primarily, premarital and preconception genetic counseling should be advocated for and made readily available, permitting couples to make informed reproductive choices. Research indicates that such counseling enhances knowledge of genetic risks and can affect reproductive decisions. Educational programs, such as marital education, sexual health education aligned with religious principles, and public awareness campaigns, can enhance communication, intimacy, and dispute resolution in couples. Furthermore, mentorship programs, in which senior couples coach newlyweds, may facilitate adaptation and resilience during the initial years of marriage. Psychosocial support, encompassing counseling services and intergenerational conversations, can mitigate the stigma associated with genetic risks and foster healthier relational dynamics. Facilitating women’s involvement in decision-making processes and guaranteeing their access to genetic information are essential. The execution of cohesive, interdisciplinary public health plans that amalgamate medical, educational, and religious sectors is necessary. Culturally appropriate interventions require continuous research, longitudinal assessments, and community involvement to guarantee sustainability and efficacy.