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 weight and nutrient deficiencies, highlighting the need for well-planned diets and supplements during pregnancy.

Study: The association of a vegan diet during pregnancy with maternal and child outcomes: a systematic review. Image credits: KieferPix / Shutterstock

This is evident from a recent study published in the journal NutrientsResearchers in the Netherlands evaluated nutritional 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 veganism, which excludes all animal products, is increasing, driven by ethical, environmental and health concerns. A 2023 European survey found that 1-8% of the population follows a vegan diet, of which 75% are women between the ages of 18 and 45. However, the increase in veganism among women of childbearing age has raised concerns about the long-term effects of vegan diets on maternal and fetal health, with evidence from existing studies being inconsistent. Maternal nutrition during pregnancy is crucial as deficiencies in nutrients such as iron, iodine and calcium can cause serious health complications. However, guidelines on vegan diets during pregnancy vary, with some organizations endorsing it if it is properly planned, while others advise against it. Further 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 in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A search was conducted in three electronic databases, PubMed, Embase, and Cochrane, from January 1, 2000 to January 24, 2024. The search strategy included a combination of Mesh terms and keywords related to vegan and vegetarian diets, as veganism is also known. a kind 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 examining the effects of a vegan diet on maternal and fetal outcomes in pregnant women. Studies involving non-pregnant participants or participants following a non-vegan diet, such as pescatarians (who eat fish but no other meat) or flexitarians (mostly vegetarian, occasionally meat), were excluded. Non-original studies, reviews, commentaries and case reports were also excluded. Importantly, no restrictions on language or outcome measures were applied due to limited data availability, highlighting the current gap in comprehensive research on this topic.

Independent reviewers screened titles and abstracts. The full texts of potentially relevant articles were retrieved and final decisions on inclusion were made after independent reviews 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 Cohort and Cross-sectional Studies. Each study was assessed for quality, with final scores categorized 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 duplicates were removed, 2,067 unique articles were screened by title and abstract, resulting in six articles included in the final review. These studies included both vegan and omnivorous participants, although results from any vegetarian groups were not considered in this review. Two studies were prospective cohort studies involving the same group of participants, while the other 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, while four also included maternal outcomes. The sample size 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 size of the studies, the authors emphasized that these results should be considered preliminary and hypothesis-generating rather than conclusive.

The studies showed varying results regarding nutrient intake. One study reported that vegan women had significantly lower protein, retinol, vitamin B12, vitamin D, calcium and iodine intake than omnivores. However, the intake of beta-carotene and folic acid was higher in vegans. While these findings are significant, the journal also highlights that the use of nutritional supplements, particularly vitamin B12 and iron, could optimize nutrient levels in vegan pregnant women, reducing some of these deficiencies. Another study found no significant differences in the plasma levels of ferritin, hemoglobin, vitamin B12, and folic acid between vegan and omnivorous pregnant women, although women on a vegan diet who took supplements had significantly higher circulating vitamin B12 levels.

Two studies reported significantly lower maternal weight gain in vegan women compared to omnivores, with fewer cases of excessive weight gain among the vegan group. However, results on maternal pregnancy-related outcomes were mixed. One study found a higher prevalence of preeclampsia (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 research is needed to assess whether these results are due to dietary factors or other confounding variables not taken into account in the studies.

In terms of fetal outcomes, five studies examined birth weight, with some reporting significantly lower birth weight and a higher prevalence of small for gestational age (SGA) babies among vegan mothers. By comparison, others found no significant differences in birth weight or SGA prevalence between the two groups. The journal’s authors suggested that the lower birth weight may be related to lower protein intake in vegan women, a factor that could influence fetal growth. One study also assessed umbilical cord nutritional levels, with no significant differences between groups, except for higher vitamin B12 levels in infants born to vegan mothers who took supplements. Overall, the results showed some differences in maternal and fetal outcomes, but findings were inconsistent between studies. This inconsistency, combined with the small sample size, limits the ability to draw firm conclusions from the existing data.

Conclusions

In summary, vegan women had lower intakes of protein, vitamin B12 and calcium, but higher levels of beta-carotene and folic acid. The use of vitamin B12 supplements has been found 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, indicating a need for supplementation across all food groups. Some studies reported lower birth weight among babies born to vegan mothers, although results on the prevalence of small pregnancies were mixed. Vegan women were less likely to experience excessive weight gain during pregnancy, but findings on preeclampsia were inconsistent. Due to the methodological limitations of the included studies, the authors call for larger, more rigorous research to develop clearer guidelines on the effects of a vegan diet during pregnancy.