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

While a vegan diet can provide essential nutrients, research shows potential risks such as low birth weight and nutrient deficiencies, highlighting the need for well-planned diet and supplements during pregnancy.

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

A new study published in the journal nutrientsDutch researchers evaluated nutrient intake and its relationship to maternal and fetal outcomes in pregnant women adhering to a vegan diet, providing evidence-based recommendations and guidelines.

Background

Veganism, which excludes all animal products, is increasing in prevalence due to ethical, environmental and health concerns. A survey conducted in Europe in 2023 found that 1-8% of the population follows a vegan diet, and 75% are women aged 18-45. However, the rise of veganism among women of reproductive age has raised concerns about the long-term effects of a vegan diet on maternal and fetal health; 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 problems. However, rules regarding vegan diets during pregnancy vary; some organizations approve of it if it is well planned, while others advise 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 performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A search was conducted between January 1, 2000 and January 24, 2024 in three electronic databases: PubMed, Embase, and Cochrane. The search strategy included a combination of Mesh terms and keywords related to vegan and vegetarian diets; It is a type of vegetarian diet found in the literature. References from 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 evaluating the effects of a vegan diet on maternal and fetal outcomes in pregnant women. Studies involving non-pregnant participants or participants following non-vegan diets such as pescatarians (who eat fish but no other meat) or flexitarians (mostly vegetarian, occasionally meat-eater) were excluded. Non-original studies, reviews, reviews, and case reports were also excluded. Importantly, no restrictions were imposed on language or outcome measures due to limited data availability; This highlights the current gap in comprehensive research on this topic.

Independent reviewers screened titles and abstracts. Full texts were retrieved for potentially relevant articles and final decisions for inclusion were made following independent reviews and discussion. Data extraction was performed and discrepancies were resolved through further review. The methodological quality of included studies was assessed using the National Institutes of Health Study Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. Each study was rated for quality, and final scores were classified as good, fair, or poor based on the rating of individual criteria. 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 being included in the final review. These studies included both vegan and omnivorous participants, but results from any vegetarian group 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 (US), and while all reported on fetal outcomes, 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. Because of the small sample sizes of the studies, the authors emphasized that these results should be viewed as preliminary and hypothesis-generating rather than definitive.

Studies have shown different results regarding nutritional intake. One study reported that vegan women’s intake of protein, retinol, vitamin B12, vitamin D, calcium, and iodine was significantly lower than omnivores. However, beta-carotene and folate intake was higher in vegans. While these findings are important, the journal also highlighted that the use of nutritional supplements, especially vitamin B12 and iron, may alleviate some of these deficiencies by optimizing nutrient levels in vegan pregnant women. Another study found no significant differences in plasma ferritin, hemoglobin, vitamin B12, and folic acid levels between vegan and omnivorous pregnant women, but women who followed a vegan diet and took supplements had significantly higher circulating vitamin B12 levels.

Two studies reported significantly lower maternal weight gain in vegan women compared to omnivores and fewer cases of excess weight gain in the vegan group. However, results regarding maternal pregnancy-related outcomes were mixed. One study found a higher prevalence of preeclampsia (pregnancy-induced high blood pressure) in vegan women, while others showed no significant differences in gestational diabetes, premature birth, cesarean section, or postpartum bleeding between vegan and omnivorous women. The journal emphasized that more research is needed to assess whether these results are due to nutritional factors or other confounding variables not taken into account in the studies.

Regarding fetal outcomes, five studies examined birth weight; some have reported significantly lower birth weight and a higher prevalence of small for gestational age (SGA) babies among vegan mothers. In comparison, others found no significant difference in birth weight or SGA prevalence between the two groups. The journal’s authors suggested that low birth weight may be linked to low protein intake in vegan women, and that this factor may affect fetal growth. One study also evaluated umbilical cord nutrient levels; There were no significant differences between groups, except for higher vitamin B12 levels in babies of vegan mothers who took the supplement. Overall, the results showed some differences in maternal and fetal outcomes, but findings were inconsistent across studies. This discrepancy, combined with small sample sizes, limits the ability to draw definitive conclusions from the available data.

Results

To summarize, vegan women had lower intakes of protein, vitamin B12, and calcium, but higher levels of beta-carotene and folate. The use of vitamin B12 supplements has been shown to be particularly effective in preventing deficiencies in both mothers and babies. However, vitamin D intake was frequently inadequate in both vegan and omnivorous women, suggesting a need for supplementation across dietary groups. Although some studies have reported lower birth weight among babies of vegan mothers, results regarding the prevalence of small for gestational age have been mixed. Rates of excess pregnancy weight gain were lower in vegan women, but findings regarding preeclampsia were inconsistent. Due to the methodological limitations of the included studies, the authors call for larger, more rigorous studies to develop clearer guidelines on the effects of a vegan diet during pregnancy.