1. Introduction
Nausea and vomiting in pregnancy (NVP) is one of the uncomfortable symptoms of women in early pregnancy. About 35–91% of pregnant women in the world will experience varying degrees of nausea or vomiting during pregnancy, generally starting at 6–8 weeks of pregnancy and ending at 16–20 weeks of pregnancy [
1,
2]. Moderate and severe nausea or vomiting, also known as hyperemesis gravidarum (HG), not only causes a decrease in the appetite of pregnant women but also causes electrolyte disorder, acid–base imbalance and even weight loss [
3], reducing the quality of sleep and life, even impairing daily function [
4,
5]. In addition, NVP, especially HG, can cause adverse pregnancy outcomes such as preterm birth, small-for-gestational-age infants and an increased risk of neurodevelopmental delay [
6], which may be due to a lack of key nutrients for the growth and development of mothers and infants [
7].
There are relatively few studies on the dietary intake of pregnant women with NVP, and most of these studies focus on HG [
6]. However, the incidence of HG is only 0.8–3.3%. Based on this fact, focusing only on HG may actually ignore a large proportion of pregnant women. Current studies have also shown inconsistent results for changes in dietary intake caused by NVP. A Norwegian study of more than 50,000 pregnant women found that women with NVP had higher intakes of energy, carbohydrates, vitamin A, folate and vitamin C [
8]. However, studies in other countries, such as South Korea [
9], Finland [
10] and the United Kingdom [
11], found that the intake of energy, macronutrients and micronutrients, as well as the diet quality, were significantly lower in women with NVP women than in those with no NVP. The inconsistency of research results may be due to cross-sectional data or different regional cultures. Moreover, there is no analysis of the association between NVP and dietary intake in China. Therefore, it is necessary to explore the association between NVP and dietary intake in Chinese pregnant women.
In conclusion, it is not clear which nutrients are key to women with NVP, the degree of nutrient deficiencies caused by NVP, the specific food groups that cause nutrient deficiencies or the nutrient intake of pregnant women with different NVP severity. Therefore, more research on the dietary intake of women with NVP is needed.
The purpose of our study was to analyze the incidence of NVP among pregnant women in the first trimester in 10 Chinese cities and the association between NVP, dietary intake and gestational weight gain.
4. Discussion
This study investigated the association between NVP and dietary intake in first-trimester pregnant women in 10 cities in China. Among the 303 pregnant women enrolled in this study, a total of 84.1% experienced NVP, which is similar to the incidence rates reported in previous NVP studies in the Chinese population: 59.6% [
16], 71.8% [
12] and 90.9% [
17]. Among pregnant women with NVP, the proportions of self-evaluated mild, moderate and severe NVP were 62.4%, 25.9% and 11.8%, respectively. Several other studies of Chinese pregnant women used the Pregnancy-Unique Quantification of Emesis and Nausea (PUQE) scale to assess the severity of NVP. These studies reported a lower proportion of mild NVP (41.4–47.5%) than this study, a higher proportion of moderate NVP (49.2–56.9%) and a similar proportion of severe NVP (1.7–8.7%) [
17,
18,
19], suggesting that the self-assessment by pregnant women tends to be mild compared with the PUQE scale, which may be due to their underestimating the severity of their own NVP.
We found that in the severe NVP group, the rate of GWG was much lower than in the non-NVP group, and half of them even experienced negative GWG. Although our study only examined weight gains in early pregnancy, studies have demonstrated that NVP in the first trimester is associated with lower GWG throughout pregnancy [
8,
12]. Moreover, studies have shown that insufficient weight gain is associated with a variety of adverse maternal and infant outcomes, such as an increased risk of gestational diabetes [
20] and low birthweight or small-for-gestational-age offspring [
21,
22,
23]. Babies born to women with inadequate weight gain had an increased risk of death within their first year of life [
24] and slower neurodevelopment later in life [
25].
This study found that pregnant women with NVP generally had a lower dietary intake of nutrients, including a variety of macronutrients, vitamins and minerals (i.e., energy, protein, fat, vitamin A, thiamin, riboflavin, vitamin E, phosphorus, potassium, iron, zinc, etc.), compared with those without NVP. We also found that pregnant women with NVP were more likely to have insufficient intake of protein, riboflavin, calcium, phosphorus and selenium. In terms of specific food groups, pregnant women in the NVP group had a lower average daily intake of mushrooms, algae, nuts and seeds, meat, eggs and dairy products. Moreover, the more serious the nausea and vomiting of the pregnant women in the early stage of pregnancy, the lower the intake of energy, all macronutrients and some micronutrients. The intake of nuts, seeds, livestock meat, poultry meat, aquatic products, eggs, dairy products and other food groups also showed a downward trend.
There are great differences in the research conclusions for the impact of NVP on the nutritional intake of pregnant women. Similar to the findings of the present studies, a study conducted in Korea [
9] and a study conducted in Finland [
10] reported a reduced intake of energy and various nutrients in pregnant women with NVP, including protein, sucrose, vitamin A, thiamin, riboflavin, vitamin B12, vitamin C, niacin, folate, calcium, iron, zinc, etc. Additionally, the more severe the NVP, the greater the reduction in nutritional intake. In terms of specific food groups, the intake of meat products and vegetables in pregnant women with NVP decreased. Furthermore, increased NVP severity was associated with a decreased intake of vegetables, tea/coffee, rice/pasta, breakfast cereals, legumes and citrus fruits/juices and an increased intake of white bread and soft drinks [
11]. However, a study conducted in Norway reported significantly different results from the present studies. The energy intake of patients with NVP was higher than that of patients with no NVP, mainly due to the increased intake of carbohydrates and added sugars. After adjustment for energy intake, the NVP group still tended to intake more of almost all types of micronutrients, as well as processed meats, vegetables, fruits and sugar-sweetened soft drinks more frequently [
8]. The reason for the inconsistency of results may be that the NVP assessment and nutrient intake assessment methods were different between studies. Moreover, the dietary habits and customs of pregnant women in different regions would also have a significant impact on the research results.
Our study found that NVP patients generally had a lower intake of B vitamins, especially thiamin and riboflavin, which is consistent with other studies. The main food sources of thiamin are grains, beans, nuts, animal offal, lean meat and eggs [
26,
27]. For pregnant women, the main manifestations of thiamin deficiency are anorexia, nausea and vomiting [
27]. Clinically, patients with severe NVP (i.e., HG) have been regarded as a high-risk group for thiamin deficiency [
26]. Thiamin is also essential for the fetus, with multiple studies showing that thiamin deficiency has negative effects on fetal brain development and may lead to fetal brain dysfunction [
28]. Furthermore, thiamin intake during pregnancy contributes to neuromotor maturation in newborns [
29]. Riboflavin is abundant in meat, milk, nuts, eggs and vegetables [
30]. Insufficient riboflavin intake during pregnancy may affect embryonic growth and cardiac development in offspring [
31]. Furthermore, studies have found that women with postpartum depression had lower serum riboflavin levels [
32]. Our study found that the intake of animal meat, nuts and seeds in pregnant women with NVP, especially severe NVP, was lower than in those with no NVP, suggesting that the aversion to these foods may lead to a reduction in thiamin and riboflavin intake, which may have potential adverse effects on the health of both mother and infant.
The potential biological mechanism of the association between NVP with nutritional intake remains uncertain. However, studies have shown that women with NVP have increased olfactory and taste sensitivity [
33], which may cause nausea from smells in the environment and from some disgusting tastes in food in order to reject any potentially toxic foods with a strong smell [
34]. This statement came from the “maternal–embryo protection hypothesis”, which links NVP to the development of taste aversion. The root of taste aversion is to avoid foods that pose a high threat to the mother and fetus, such as meat, poultry, fish/seafood and eggs [
34,
35]. Our study also found that the intake of meat and eggs in women with NVP is lower than in those with no NVP. However, these foods tend to be good sources of high-quality protein [
36,
37] and are essential for fetal growth and development [
38]. Therefore, the poor nutrition intake of women with NVP we observed may be due to mothers’ aversion to some certain foods. They choose to avoid or eat certain foods less to control their nausea or vomiting symptoms. However, after all, this study is a cross-sectional study; thus, we cannot deny the possibility that nutrition intake affects NVP symptoms. For example, many studies have proved that vitamin B6 supplements have a good effect on the treatment of NVP symptoms [
39]. Similar therapeutic effects were found in quince [
40] and ginger [
41].
Based on the multicenter data, our study investigated the incidence of NVP in first-trimester Chinese women and explored its association with dietary nutrients and food intake in Chinese women for the first time. The selection of ten cities based on the economic level and geographical location allowed better extrapolation of our study conclusions.
However, this research does have some limitations. Firstly, this study is a cross-sectional study, which limits causal inference. It cannot be excluded that changes in the dietary intake of pregnant women have an impact on the occurrence of nausea and vomiting. Secondly, the survey is mostly based on the self-reported data of pregnant women, which may lead to recall bias. Moreover, an in-person interview may be associated with a higher risk of social desirability bias compared to a self-administered questionnaire. Additionally, nausea and vomiting were not assessed by means of a validated tool such as the PUQE but were self-reported. Finally, the occurrence of maternal nausea or vomiting and dietary intake is a dynamic process, while further prospective cohort monitoring is needed to explore the relationship between them. We also need to explore whether the history of NVP during early pregnancy will have a certain impact on the nutrition intake in the middle or later stage of pregnancy through long-term follow-up observation.