The Impact of Genital Infections on Women’s Fertility

Abstract

Sexually transmitted infections (STIs) are a significant global health concern, affecting millions of people worldwide, particularly sexually active adolescents and young adults. These infections, caused by various pathogens, including bacteria, viruses, parasites, and fungi, can have profound implications for women’s reproductive health and fertility. This review explores the role of vaginal and uterine infections in women’s infertility, focusing on the most common pathogens and their impact on reproductive outcomes. Bacterial infections, such as those caused by intracellular bacteria (Mycoplasma, Ureaplasma, and Chlamydia), Neisseria gonorrhoeae, and bacterial vaginosis, are among the most prevalent causes of infertility in women. Studies have shown that these infections can lead to pelvic inflammatory disease, tubal occlusion, and endometrial damage, all of which can impair fertility. Mycobacterium tuberculosis, in particular, is a significant cause of genital tuberculosis and infertility in high-incidence countries. Viral infections, such as Human papillomavirus (HPV) and Herpes simplex virus (HSV), can also affect women’s fertility. While the exact role of HPV in female infertility remains unclear, studies suggest that it may increase the risk of endometrial implantation issues and miscarriage. HSV may be associated with unexplained infertility. Parasitic infections, such as trichomoniasis and schistosomiasis, can directly impact the female reproductive system, leading to infertility, ectopic pregnancy, and other complications. Fungal infections, such as candidiasis, are common but rarely have serious outcomes related to fertility. The vaginal microbiome plays a crucial role in maintaining reproductive health, and alterations in the microbial balance can increase susceptibility to STIs and infertility. Probiotics have been proposed as a potential therapeutic strategy to restore the vaginal ecosystem and improve fertility outcomes, although further research is needed to establish their efficacy. In conclusion, vaginal and uterine infections contribute significantly to women’s infertility, with various pathogens affecting the reproductive system through different mechanisms. Early diagnosis, appropriate treatment, and preventive measures are essential to mitigate the impact of these infections on women’s reproductive health and fertility.

1. Introduction

Sexually transmitted infectious diseases (STDs) represent a significant epidemiological problem that affects the population across the board, precisely because of their mode of transmission and spread. In 2024, the World Health Organization (WHO) stated that, worldwide, more than one million sexually transmitted infections (STIs) are acquired every day among people aged 15 to 49 years [1]. STIs mainly affect sexually active adolescents between the ages of 15 and 24 years due to frequent variations in sexual partners and low condom use [2]. The epidemiology of STIs is inaccurate, as these infections often remain asymptomatic and, therefore, go untreated, and surveillance records across countries are incomplete [1]. These infections can be caused by more than thirty different pathogens of bacterial, fungal, parasitic, and viral nature and can have implications not only for the state of health but also for fertility status [3]. The impact that some pathogens of the female lower genital tract have on infertility is now well known, so much so that specific protocols have been developed that are currently in use in many assisted reproductive technologies (ART) centers around the world [4]. However, the role of other pathogens in infertility remains poorly understood and is currently the subject of debate [5,6,7].

Thus, this literature review aims to summarize the main evidence on the impact of microorganisms on women’s reproductive health and fertility. Particular attention was given to the role of the vaginal microbiome and its alterations in increasing susceptibility to infections, as well as to the potential therapeutic effects of probiotic-based interventions. The review was conducted through a non-systematic literature search using the databases PubMed, Scopus, and Web of Science. The search included articles published up to June 2025, written in English, and focusing on the relationship between genital infections and female infertility. Among the keywords used were “female infertility”, “sexually transmitted infections”, “vaginal microbiota”, “genital infections”, and “probiotics”. Case reports, case series, commentaries, letters to the editor, editorials, and conference abstracts were excluded from the selection.

2. Bacterial Infections

Many bacterial infections can affect the vaginal environment. In particular, the bacteria that can colonize the genital environment are divided into two large categories: intracellular bacteria, referred to as Mycoplasma, Ureaplasma, and Chlamydia, and extracellular bacteria [8]; among the latter, a relevant role in the pathogenesis of infections of the female genital tract is played by the bacteria responsible for bacterial vaginosis (BV) [9,10]. All these infections can have varying implications on fertility [11].

2.1. Intracellular Bacteria: Mycoplasma, Mycobacterium tuberculosis and Chlamydia

Intracellular bacteria include Mycoplasma spp. and Chlamydia. All these bacteria are united by the characteristic of being obligate aerobes or facultative aerobes/anaerobes that binds them to intracellular life [12]. These bacteria share a common feature that distinguishes them from many other types of microorganisms: they either require oxygen to survive (obligate aerobes) or are capable of adapting to both oxygen-rich and oxygen-poor environments (facultative aerobes or anaerobes). This physiological trait is closely linked to their ability, and often necessity, to live within host cells. Their intracellular lifestyle provides a controlled environment that supports their growth and reproduction, compensating for their limited metabolic capabilities and often providing protection from the host’s immune system.

2.1.1. Mycoplasma and Ureaplasma

Genital mycoplasmas belong to the Mollicutes family, characterized by their extremely small size and the absence of a cell wall [13]. Among these, the most relevant for human health are Mycoplasma genitalium, Mycoplasma hominis, Ureaplasma parvum, and Ureaplasma urealyticum. These microorganisms can colonize the urogenital tract, often without causing obvious symptoms [14]. The most frequent symptoms in women are related to abnormal or purulent vaginal discharge, pain in the lower abdomen, and bleeding following sexual intercourse [13]. The presence of those bacteria in the endocervix can disrupt the vaginal ecosystem and may contribute to the development of more severe infections. Antibiotic therapy is based on the administration of azithromycin or erythromycin [15]. Abnormal vaginal microbiota has been linked to BV through its stimulation of proinflammatory cytokines [16]. Furthermore, this disrupted microbiota can silently ascend into the uterus, causing notable inflammation of the endometrium and triggering immune responses [9]. In a study by Nazarzadeh et al., a cohort of 160 women underwent a vaginal swab for Mycoplasma hominis; among these, 80 were considered fertile and assigned to the control group, and 80 considered infertile were instead assigned to the pathological group. Among the patients in the control group, only 5 (6.25%) had a positive swab for M. hominis (6.25%), while among the patients belonging to the pathological group, 29 (36.25%) were infected. This data supports the idea that M. hominis infection may have implications for patients’ fertility [14]. Similarly, Moridi et al. highlighted that the prevalence of endocervical M. genitalium, U. urealyticum, and M. hominis in infertile women (12.73%, 19.58%, and 10.81%) was higher than in fertile women (3%, 10.85%, and 4.35%) [17]. Also, in another study by Ezeanya-Bakpa et al., a sample of 100 women, of whom 31 were infertile, underwent an endocervical swab for Mycoplasma infections, and also, in this case, it emerged that among infertile women, the prevalence was 6.45% for M. hominis and 3.23% for U. urealyticum, and all M. hominis isolates from asymptomatic women were found to be genetically related to those of infertile women [18]. Mycoplasma infections have also been associated with infertility events from suspected tubal factors, as suggested by Rita Piscopo et al. in a 2020 retrospective cross-sectional study conducted on 245 women who underwent hysterosalpingography and endocervical swabs for Mycoplasma and Chlamydia. In particular, it emerged that the prevalence of tubal factor infertility was significantly higher in Mycoplasma hominis-positive women [15]. A study analyzed the titer of IgG, IgM and IgA against Treponema pallidum, U. urealyticum, and M. hominis in the serum of 308 patients who underwent treatment for infertility and showed that overall, 6.4%, 4.6% and 49.0% of patients tested positive for T. pallidum, U. urealyticum, and M. hominis, respectively, suggesting more of an association between these infections and the rate of infertility in women [12]. However, another study contrasts with these results by demonstrating a more significant association between M. hominis in women with BV, suggesting that it is the latter condition that leads to infertility [13].

2.1.2. Mycobacterium tuberculosis

Mycobacterium tuberculosis, in addition to being the primary causative agent of pulmonary tuberculosis, can also cause extrapulmonary infections, including genital tuberculosis (GTB) [19]. This form is particularly relevant in women of childbearing age, where it can represent an unexplained cause of infertility [20]. Transmission occurs mainly by hematogenous or lymphatic spread from a primary tuberculosis infection, often pulmonary, rather than by direct contact with the pathogen [21]. Diagnosis is usually made by detecting acid-resistant bacilli under a microscope, culturing on endometrial biopsy, or histopathological examination showing epithelioid granulomas in the biopsy [22]. Genital infections can involve several structures of the reproductive system: in 90% of cases, fallopian tubes are involved, and this leads to tubal occlusion, which can cause infertility or ectopic pregnancies [23]; the endometrium is involved in 50–60% of cases, and tuberculous endometritis can cause menstrual irregularities, amenorrhea, or infertility [19,22]; ovaries are involved in 20–30% of cases, and ovarian infections can form tumor-like pelvic masses [24]; finally, the cervix and vagina are rarely involved (less than 5%), but may mimic chronic neoplastic or inflammatory diseases [25]. However, functional or non-structural alterations may also contribute to reduced fertility. The heightened production of inflammatory cytokines in GTB can lower the receptivity of the endometrial lining and interfere with embryo implantation [20]. Moreover, when the ovaries are affected, GTB may decrease ovarian reserve and lead to problems with ovulation or hormonal imbalances in some instances [26]. Many studies have confirmed the role of Mycobacterium tuberculosis infection in the fertility status of women. In a survey conducted by Melkamu et al. on 122 women with a histopathological diagnosis of GTB, it was found that in the majority of cases of tuberculous endometritis (53.3%), histopathology revealed early-stage granulomas. Acid-resistant bacilli were found in a significant proportion (42.6%) of female GTB tissues with histopathological features of tuberculosis. The ovary showed the highest detection rate of acid-resistant bacilli, followed by fallopian tubes, endometrium, and cervix [24]. In a study conducted by Saxena et al. on 43 women with a confirmed diagnosis of tubal infertility, 6 received a definite diagnosis of GTB [27]. Similarly, in a study of 185 women seeking treatment for infertility by Naik et al., simultaneously subjected to different diagnostic methods for M. tuberculosis infection (ultrasound, tuberculin skin test, and erythrocyte sedimentation rate), probable GTB was identified in 29 (15.7%) women, with 6 (21%) confirmed by all the different tests and 23 (79%) probable, not confirmed in each test [28]. In a meta-analysis of 42 studies selected with a total of 30,918 infertile women, the overall prevalence of female GTB was 20%, and the overall prevalence of infertility, primary infertility, and secondary infertility in the female GTB population was 88%, 66%, and 34%, respectively [25]. In another study, the role of female GTB and latent GTB on ovarian reserve function was investigated, suggesting their negative impact on both ovarian reserve and ovarian response to gonadotropin treatment [29]. The medical antibiotic therapy, based on isoniazid, rifampicin, pyrazinamide, and ethambutol, planned for a total treatment duration of six months, appears to have positive implications for the fertility rate of patients [22]. However, even after multimodal therapy, infertile women with GTB have low conception rates and a significant risk of complications, such as ectopic pregnancy and miscarriage [23]. In addition, conflicting data emerge in other studies that suggest a negative role of antibiotic therapy on the fertility rate of women [30]. In a systematic review, it was seen that the current antibiotic medical therapy planned for the treatment of this pathology for 6–12 months seems to have little or no effect on pregnancy, full-term pregnancy, abortion, intrauterine death, and ectopic pregnancy in women who have not reported structural consequences, while in women with apparent structural damage, antituberculosis treatment could reduce the pregnancy rate [31]. Innovative studies have been conducted to analyze the vaginal microbiota in search of potential alterations caused by GTB infection. In particular, it has emerged that in this case, the state of dysbiosis is more pronounced with a prevalence of Lactobacillus iners than of Lactobacillus crispatus, two species of lactobacilli that are physiologically present in moderate amounts in the vaginal microbiota but that increase in response to inflammatory insult, especially when Mycobacterium tuberculosis invades the endometrium [26].

2.1.3. Chlamydia

Female genital infections from Chlamydia trachomatis are one of the most common STDs globally [32]. This bacterial infection can affect several organs in the female genital tract, including the cervix, uterus, fallopian tubes, and ovaries [33]. Chlamydia is often asymptomatic, making early recognition and timely treatment difficult [34]. As a result, many women can become infected without knowing it and run the risk of developing serious complications [35]. When symptoms occur, they may include abnormal vaginal discharge, pain during sexual intercourse, or pelvic pain [36]. The diagnosis is usually made through urine tests or samples taken from the cervix, which are later analyzed via DNA amplification techniques such as polymerase chain reaction (PCR) [37]. If left untreated, a Chlamydia infection can lead to several serious complications [38]. The most common and feared is pelvic inflammatory disease (PID), which can damage the fallopian tubes and lead to infertility [39]. Other possible complications include scarring in the pelvic tissues, which can cause reproductive problems [32]. In addition, Chlamydia may increase women’s vulnerability to contracting other STDs [37,40]. The role of Chlamydia infection in infertility has been widely reported in the literature. In a study conducted by Vaikundam Subramanian et al. on 50 patients, 43 (86%) had primary infertility and 7 (14%) had secondary infertility. Three (6%) tested positive for C. trachomatis by real-time PCR, of which two had primary infertility and one had secondary infertility [41]. Fortunately, Chlamydia infection is treatable with antibiotics [33]. The most common medications used include azithromycin, administered as a single dose, or doxycycline, which must be taken over 7 days [33]. Both people involved in a sexual relationship must be treated to avoid reinfection [33,42]. In addition, it is recommended to avoid sexual intercourse during treatment until the infection has completely healed [43]. A study conducted by Chen et al. suggests that women with tubal infertility and C. trachomatis infection have a vaginal microbiota dominated by Lactobacillus iners rather than Lactobacillus crispatus and show a decrease in Lactobacillus, Bifidobacterium, Enterobacter, Atopobium, and Streptococcus, accompanied by a reduction in cytokine levels such as interferon (IFN)-g and interleukin (IL)-10 [35]. Therefore, an important therapeutic strategy could be to restore the vaginal ecosystem to a state of eubiosis after treating the infection with the intended antibiotic therapy [44].

2.2. Neisseria gonorrhoeae

Neisseria gonorrhoeae infection is among the most common STIs globally [40]. It is a Gram-negative bacterium that mainly infects the mucous membranes of the genitals but can also affect the throat, rectum, and eyes [10]. It is transmitted through unprotected sexual contact with an infected person, including vaginal, anal, and oral intercourse [45]. The clinic is often very nuanced and non-specific. In women, symptoms, when noticeable, may include abnormal vaginal discharge, pain during sexual intercourse, intermenstrual bleeding, and pelvic pain [46]. If left untreated, gonorrhea can lead to serious complications such as PID, which can cause infertility and can also increase the risk of contracting other STIs [10]. In the case of PID, the pathogenesis is probably linked to damage to the pathogen that causes inflammation and subsequent loss of cilia of the hair cells of the fallopian tubes; in this regard, human fallopian tubes express the receptor for IL-17C on the epithelial surface and treatment with purified IL-17C induces the secretion of proinflammatory cytokines, as well as desquamation of the epithelium and generalized tissue damage. These results demonstrate a critical, previously unrecognized role of IL-17C in the harmful inflammation induced by gonococcus in a human model of PID [46]. In addition, a study of women with PID induced by N. gonorrhoeae and/or C. trachomatis with histological endometritis revealed activation of myeloid cells, cell death, and innate inflammatory pathways, along with a reduction in T cell activation, supporting the central role of the inflammatory process in the mechanisms of fertility impairment in women [45]. The diagnosis of gonorrhea is generally based on microbiological tests, such as culture, PCR, and DNA amplification tests, from samples taken using endocervical swabs [45]. Current guidelines suggest treatment using a combination of antibiotics, usually ceftriaxone and azithromycin, to counteract bacterial resistance to be extended to sexual partners [40].

2.3. Bacterial Vaginosis

BV is the most common vaginal infection in women of childbearing age and is caused by an imbalance in the normal vaginal bacterial microbiota [9]. BV is not considered an STD, although it is more common in sexually active women. It is caused by an imbalance of the bacteria normally present in the vagina, rather than by a single pathogen, as is the case with STDs. Under normal conditions, the vagina is predominantly colonized by lactobacilli, which help maintain an acidic environment and protect against infection [47]. However, in BV, the overgrowth of anaerobic bacteria, such as Gardnerella vaginalis, Atopobium vaginae, Mobiluncus spp., and other opportunistic microorganisms, alters this microbiota, leading to characteristic symptoms [11]. Many women with BV may be asymptomatic, but when present, the most common symptoms include heavy, grayish-white vaginal discharge; an unpleasant odor, often described as a “fishy odor,” which becomes more noticeable after sexual intercourse; and, less commonly, vaginal itching or irritation [48]. The diagnosis of BV is typically made through clinical examination using the Amsel criteria, vaginal pH greater than 4.5, and microscopic observation of clue cells, which are epithelial cells of the vagina that appear covered with bacteria [49]. It is also valuable to combine endovaginal swabs to search for Gardnerella vaginalis or other bacteria usually associated with this condition [11].

Treatment involves the use of antibiotics, such as metronidazole or clindamycin [11]. Fluorescent in situ hybridization (FISH) studies have shown that BV is associated with the formation of biofilms dominated by Gardnerella spp. on the vaginal mucosa. These biofilms are implicated, among other things, in a partial failure of antibiotic therapy and appear to be at the basis of frequent recurrences [9]. Therefore, in some cases, the use of probiotics may be beneficial in restoring the balance of the vaginal microbiota [50]. Although BV is generally not dangerous, it can increase the risk of contracting STDs or post-surgical infections, especially following gynecological surgeries, or pregnancy complications such as premature birth and low birth weight [51]. There does not seem to be a significant association between BV and infertility. However, a cohort study conducted on 163 patients seeking pregnancy showed that 27% of participants were diagnosed with BV, which prolonged the time to conception [46].

3. Viral Infections

Viral infections of the genital tract are caused by viruses, which can lead to complications if not adequately treated [52,53]. Among the most common are Human papillomavirus (HPV), genital herpes viruses, and Molluscum contagiosum [53]. However, among these, the first two can have a significant impact on a woman’s fertility [54].

3.1. Human Papillomavirus

HPV is one of the primary pathogens of the female genital tract [2]. It can cause genital warts and, in some cases, precancerous lesions, especially in the cervix, that are often asymptomatic [55]. Transmission occurs mainly by sexual contact [56]. Vaccination against both high-risk HPV types (HPV-16, -18, -31, -33, -45, -52, and -58) and low-risk types (HPV-6 and -11) offers an essential opportunity for prevention [57]. Treatment consists of removing the lesions with cryotherapy, laser, or topical treatments [58]. The exact role of HPV infection on the female fertility rate has not yet been clarified. HPV can affect female fertility mainly through an increased risk of miscarriage and alteration of endometrial trophoblastic cell implantation. In addition, association with vaginal bacterial dysbiosis, particularly with Gardnerella vaginalis, or co-infection with other STI agents may further aggravate the adverse effects of HPV on fertility. In another study, it was shown that HPV infection can migrate along the female genital tract, involving the endometrium and ovaries, and could play a role in the genesis of pelvic endometriosis; moreover, HPV has a slight impact on the kinetics of embryo development in vitro, although without affecting the rate of live births [58]. In a case–control study in which cervical samples were analyzed on 95 women followed in a fertility center, it was found that among all the agents surveyed, only HPV infection showed a significant difference between infertile and fertile women, suggesting a possible increased risk of female infertility [57]. However, another study, conducted by Carullo et al. in 2024 on 145 couples, showed that the cumulative rates of live birth by egg retrieval in couples in which both partners were negative or positive did not differ, 37% and 44%, respectively [54].

3.2. Herpes Virus

Genital Herpes simplex virus (HSV) infections, particularly HSV-1 and HSV-2, represent one of the most common STIs [56]. Of the two, HSV-2 is the main culprit of genital herpes, while HSV-1, traditionally associated with oral herpes, can also cause genital infections [59]. The infection may be asymptomatic or manifest itself with symptoms such as skin lesions (painful blisters that turn into open ulcers on the vulva, vagina, and cervix), itching and burning, especially during urination, and pelvic pain, sometimes associated with enlargement of the inguinal lymph node stations [60]. After the initial infection, the virus remains latent in the nerve ganglia and can reactivate periodically, especially during stress, immunosuppression, menstrual cycles, or concomitant diseases [2]. Diagnosis is made by clinical examination and specific PCR tests, combined or not with serological research for identifying antibodies against HSV-1 and HSV-2 [52]. Among the complications, we may have a greater predisposition to other STDs or maternal–fetal transmission during childbirth with possible neurological impairments, even lethal, of the newborn [53]. There is no definitive cure. Drugs such as acyclovir, valacyclovir, and famciclovir can reduce the severity of symptoms and the rate of recurrence and transmission to the newborn during childbirth [2]. In a 2021 study, an attempt was made to investigate the role that HHV-6 plays in association with these pathogens [5]. However, in a survey conducted in 2022 on a sample of 299 patients undergoing infertility treatments, it was shown that HSV-2 was more common in patients with secondary infertility (14.1%) than in primary infertility (9.2%) [59]. A possible explanation could be related to the fact that vaginal viruses actively interact with the vaginal bacterial microbiota, directly infecting the bacteria that are part of it and also engaging with the host’s immune system, as suggested by Happel et al. [53].

4. Parasitic Infections

Parasitic infections of the genital tract are many, some caused directly by vaginal pathogens, others caused by systemic pathogens that only secondarily affect the female genital tract [2]. Among the latter is ascariasis, an infectious parasitic disease of the gastrointestinal tract with secondary vaginal involvement and direct effects on primary infertility. The presence of Ascaris lumbricoides parasites in a woman’s body may be a contributing factor in the development of various types of infertility, including tubal, tubal-peritoneal, and endocrine-related forms [61]. This association is believed to stem from the harmful effects of toxic substances released by Ascaris lumbricoides, which can negatively affect key endocrine organs such as the thyroid gland, ovaries, and adrenal glands [2]. These disruptions may interfere with normal hormonal regulation, ovulation, and reproductive function, thereby compromising a woman’s fertility [61]. As demonstrated in a study conducted by Sklyarova et al., ascariasis plays a role in hormonal imbalances, endothelial–lymphocyte dysfunction, and intestinal dysbiosis, with repercussions on vaginal dysbiosis and the proliferation of subsequent opportunistic flora, all of which predispose to a state of primary infertility [61]. Another parasite that can affect the female genital tract is schistosomiasis and ectopic deposition of Schistosoma eggs, observed in some cases also at the level of the ovaries and fallopian tubes, which can cause damage to the reproductive organs and complications such as infertility, ectopic pregnancy, miscarriages, premature birth, low birth weight, and maternal death [62].

Trichomonas Vaginalis

Parasitic infections of the vagina are mainly caused by Trichomonas vaginalis, a flagellated protozoan responsible for trichomoniasis, one of the most prevalent STIs globally [63]. This infection can cause symptoms such as copious, yellow-green, and unpleasant-smelling vaginal discharge; itching; burning; pain during sexual intercourse or urination; and specific signs such as “strawberry cervix”, the appearance of the cervix when it presents with red spots or scattered petechiae on its surface, resembling the seeds on the surface of a strawberry [64]. However, many women may be asymptomatic, thus increasing the risk of transmission [65]. Trichomoniasis is associated with complications such as infertility, increased risk of contracting other STIs, and chronic inflammation of the vaginal mucosa [66]. Diagnosis is based on microscopic examination of vaginal secretion, culture, or molecular tests such as PCR [66]. The treatment of choice is metronidazole or tinidazole, administered orally [64]. The role of Trichomonas vaginalis in infertility has not yet been perfectly clarified. However, a study by Surya et al. has shown that out of 9 women with vaginal trichomoniasis, 1 (11%) is also infertile [66].

5. Fungal Infections

Candida spp., especially Candida albicans, is naturally present in small amounts in the vaginal microbiota [67]. However, when there is an imbalance in the body’s defense mechanisms or in the factors that regulate the vaginal microbiota, the fungus can proliferate and cause an infection [68]. They are very common infections but rarely have severe outcomes. They are easily treated with topical or oral fluconazole-based therapy [63]. However, in a systematic review of the literature and meta-analysis that included eight studies conducted between 1995 and 2021 on 909 infertile patients, no association with Candida infection was demonstrated [68].

6. Role of Probiotics

The infections discussed are substantially linked to imbalances in the vaginal bacterial microbiota that increase susceptibility to these pathogens. Consequently, an alteration of the vaginal microbiome has a direct effect on the woman’s fertility status [69]. The administration of probiotics, i.e., live microorganisms that, if taken in adequate quantities, confer benefits to the host’s health, could provide a protective role in this regard [50]. Emerging evidence suggests that probiotics may be supportive in addressing specific causes of infertility, particularly those related to the reproductive tract microbiome [60]. A balanced vaginal and gut microbiota is essential for maintaining reproductive health, and disruptions, such as BV or chronic inflammation, have been linked to infertility, recurrent miscarriages, and poor outcomes in ART [3].

Probiotics, particularly strains such as Lactobacillus crispatus and Lactobacillus rhamnosus, can help restore microbial balance, enhance local immunity, and reduce pathogenic colonization in the vaginal and gastrointestinal tracts [70]. In a study analyzing twenty-six articles on patients undergoing ART, it was found that a microbiota dominated by lactobacilli, particularly the presence of Lactobacillus crispatus, is associated with a higher fertility rate; this finding confirms that a state of vaginal eubiosis plays a crucial role, even when ART is used [70]. Furthermore, the abundance of L. crispatus also plays a role in the composition of the endometrial microbiota. A study that analyzed 141 infertile women in whom the first cycle of In Vitro Fertilization (IVF) was unsuccessful demonstrated that compared to women in whom these treatments were successful, there was a lower relative abundance of L. crispatus, especially in cases of secondary infertility [71]. Additionally, probiotics may improve metabolic and hormonal profiles in women with polycystic ovary syndrome (PCOS), a common cause of anovulatory infertility. In a cross-sectional study conducted on 89 patients with PCOS, it was shown that the vaginal microbiome plays a key role in the manifestation of specific characteristic symptoms of the syndrome, such as acanthosis nigricans, intermenstrual bleeding, and elevated levels of testosterone and anti-Müllerian hormone. In all these patients, a relative increase in the abundance of L. crispatus and a reduction in L. iners were observed [72]. A study conducted by Schenk et al. showed that 40 infertile patients treated with probiotics had reduced growth of Ureaplasma parvum compared to untreated patients [73]. A study conducted on 74 women before embarking on treatment for infertility showed that a treatment based on vaginal probiotics in itself does not improve the fertility rate. Still, an extension of the therapy from one to three months allows for a better rebalancing of the vaginal microbiota. It could, therefore, be a valid hypothesis for treatment to postpone IVF when a more balanced vaginal microbiota is present [74]. In conclusion, despite the numerous published studies on the use of probiotics for vaginal dysbiosis and their actual empirical use, especially for infertile patients, there is still no clear answer that justifies their recommendation [50]. While further research is needed to fully understand the scope of their benefits, incorporating probiotics into fertility treatment regimens may offer a low-risk, supportive strategy for improving reproductive outcomes.

7. Conclusions

From this literature review, it emerged that many vaginal infections can impact the fertility status of women and couples in general. However, in not all cases was a strong and unequivocal correlation found between specific pathogens and reproductive success, particularly in women. Therefore, further studies are necessary to provide a more comprehensive definition of the topic.