How does a vegan diet during pregnancy affect mother and baby?

Although a vegan diet can provide essential nutrients, research shows potential risks, including lower birth weights and nutritional deficiencies, emphasizing the need for well-planned diets and supplements during pregnancy.

Study: Association of Vegan Diet during Pregnancy with Maternal and Child Outcomes: A Systematic Review. Image Credit: KieferPix / Shutterstock

In a recent study published in the journal Nutrientsresearchers in the Netherlands assessed nutrient intake and its association with maternal and fetal outcomes in pregnant women following a vegan diet, providing evidence-based recommendations and guidelines.

Background

The prevalence of vegetarianism, which excludes all animal products, is rising, driven by ethical, environmental and health concerns. A European survey in 2023 showed that 1-8% of the population follows a vegan diet, and that 75% are women aged 18-45. However, the rise of veganism among women of reproductive age raises concerns about the long-term effects of vegan diets on maternal and fetal health, and evidence from existing studies is inconsistent. Maternal nutrition is critical during pregnancy, as deficiencies in nutrients such as iron, iodine and calcium can cause serious health complications. However, the guidelines for vegan diets during pregnancy vary, with some organizations endorsing it if it is well planned, and others advising against it. More research is needed to clarify the long-term effects of a vegan diet on maternal and child health.

About the study

The systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Three electronic databases, PubMed, Embase, and Cochrane, were searched from 1 January 2000 to 24 January 2024. The search strategy included a combination of mesh terms and keywords related to vegan and vegetarian diets, as sometimes referred to as veganism. type of vegetarian diet in literature. References from the included studies and other systematic reviews were also screened for relevant studies, and the search results were transferred to Rayyan for management.

The review focused on original studies that assessed the effects of a vegan diet on maternal and fetal outcomes in pregnant women. Studies involving non-pregnant participants or participants on non-vegan diets, such as pescatarians (who eat fish but no other meat) or flexitarians (mostly vegetarians, occasional meat) were excluded. Non-original studies, reviews, commentaries and case reports were also issued. Importantly, no restrictions were imposed on language or outcome measures due to limited data availability, reflecting the current gap in comprehensive research on this topic.

Titles and abstracts were screened by independent reviewers. Full texts were retrieved for potentially relevant articles, and final decisions for inclusion were made after independent review and discussion. Data extraction was performed, and discrepancies were resolved by further review. The methodological quality of the included studies was assessed using the National Institutes of Health Study Quality Assessment Tool for Observational Cohorts and Cross-sectional Studies. Each study was rated for quality, with final scores classified as good, fair or poor based on individual criteria ratings. The authors noted that the quality of most studies was inadequate due to small sample sizes, self-reported data, and lack of adjustment for confounding variables.

Study results

A total of 2,211 studies were identified during the initial search. After removing duplicates, 2,067 unique articles were screened based on title and abstract, resulting in six articles included in the final review. Both vegan and omnivore participants were included in these studies, although the results of any vegetarian group were not considered in this review. Two studies were prospective cohort studies involving the same group of participants, and the remaining four were cross-sectional studies. These studies were conducted in Israel, Italy, Denmark, and the United States of America (USA), and all reported on fetal outcomes, and four also included maternal outcomes. Sample sizes ranged from 18 to 234 women on a vegan diet and 15 to 65,872 women on an omnivorous diet. Due to the small sample sizes of the studies, the authors emphasized that these results should be viewed as preliminary and hypothesis-generating rather than definitive.

The studies showed different results regarding nutrient intake. One study reported that vegan women had significantly lower intakes of protein, retinol, vitamin B12, vitamin D, calcium and iodine than omnivores. However, beta-carotene and folate intake was higher in vegans. Although these results are significant, the journal also showed that the use of dietary supplements, especially vitamin B12 and iron, could optimize nutrient levels in vegan pregnant women, thereby mitigating some of these deficiencies. Another study found no significant differences in plasma levels of ferritin, hemoglobin, vitamin B12, and folic acid between vegan and omnivorous pregnant women, although circulating vitamin B12 levels were significantly higher in women on vegan diets taking supplements.

Two studies reported a significant increase in lower maternal weight in vegan women compared to omnivores, with fewer cases of excessive weight gain among the vegan group. However, findings on pregnancy-related maternal outcomes were mixed. One study found a higher prevalence of pre-eclampsia (pregnancy-related high blood pressure) in vegan women, while others showed no significant differences in gestational diabetes, preterm birth, Cesarean sections, or postpartum hemorrhage between vegan and omnivorous women. The journal emphasized that further investigation is needed to assess whether these findings are due to nutritional factors or other confounding variables not accounted for in the studies.

Regarding fetal outcomes, five studies examined birth weight, and several reported significantly lower birth weights and a higher prevalence of small for gestational age (SGA) infants among vegan mothers. In comparison, others found no significant differences in birth weight or prevalence of SGA between the two groups. The authors of the journal suggested that the lower birth weight could be linked to a lower protein intake in vegan women, a factor that could influence fetal growth. Umbilical cord nutrition levels were also assessed in one study, with no significant differences between the groups, except for higher vitamin B12 levels in infants of vegan mothers who took supplements. Overall, the results showed some differences in maternal and fetal outcomes, but results were inconsistent across studies. This inconsistency, combined with the small sample sizes, limits the ability to draw firm conclusions from the existing data.

Conclusions

In summary, vegan women had lower protein, vitamin B12 and calcium intakes but higher beta-carotene and folate levels. The use of vitamin B12 supplements has been shown to be particularly effective in preventing deficiencies in both mothers and infants. However, vitamin D intake was often insufficient in both vegan and omnivorous women, suggesting the need for supplementation across dietary groups. Some studies have reported lower birth weights among children of vegan mothers, although the results on small-for-pregnancy prevalence have been mixed. Vegan women had lower rates of excess weight gain in pregnancy, but the results for pre-eclampsia were inconsistent. Due to the methodological limitations of the included studies, the authors call for more and more rigorous research to develop clearer guidelines regarding the effects of a vegan diet during pregnancy.