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

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

In a recent study published in the journal Nutrients, researchers in the Netherlands evaluated the nutritional intake and its association with maternal and fetal outcomes in pregnant women adhering to a vegan diet, providing evidence-based recommendations and guidelines.

Background

The prevalence of veganism, which excludes all animal products, is rising, driven by ethical, environmental, and health concerns. A 2023 European survey revealed that 1-8% of the population follows a vegan diet, with 75% being women aged 18-45. However, the rise in veganism among women of reproductive age has raised concerns regarding the long-term effects of vegan diets on maternal and fetal health, with evidence from existing studies being inconsistent. Maternal nutrition during pregnancy is critical, 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 well-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 of three electronic databases, PubMed, Embase, and Cochrane, was performed 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 veganism is sometimes referred to as a type of vegetarian diet in the 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.

Protein intake discrepancy: Nearly half of the vegan women studied had insufficient protein intake compared to recommendations, with an average of only 10.4% of daily energy intake coming from protein, which could influence fetal growth.

The review focused on original studies assessing 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 vegetarian, occasional meat), were excluded. Non-original studies, reviews, comments, and case reports were also excluded. Importantly, no restrictions on language or outcome measures were applied due to the limited data availability, which underscores 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 on inclusion were made after independent reviews and discussion. Data extraction was conducted, and discrepancies were resolved through 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 rated for quality, with final scores categorized as good, fair, or poor based on the ratings of individual criteria. The authors noted that the quality of most studies was insufficient 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 based on title and abstract, resulting in six articles being included in the final review. These studies included both vegan and omnivore participants, though the results of 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 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 conclusive.

Supplementation benefits: Vegan mothers who took vitamin B12 and iron supplements had significantly higher levels of these nutrients in both maternal and umbilical cord blood, reducing the risk of deficiencies in their babies.

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, beta-carotene and folate intake were higher in vegans. While these findings are significant, the journal also highlighted that the use of dietary supplements, particularly vitamin B12 and iron, could optimize nutrient levels in vegan pregnant women, 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, though women on vegan diets taking 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 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 results are due to nutritional factors or other confounding variables not accounted for in the studies.

Regarding fetal outcomes, five studies examined birth weight, with some reporting 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 SGA prevalence between the two groups. The authors of the journal suggested that the lower birth weight may be linked to lower protein intake in vegan women, a factor that could influence fetal growth. Umbilical cord nutrient 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 the findings were inconsistent across studies. This inconsistency, combined with the small sample sizes, limits the ability to draw firm conclusions from the existing data.

Conclusions

To summarize, vegan women had lower protein, vitamin B12, and calcium intakes but higher beta-carotene and folate levels. The use of vitamin B12 supplements was shown to be particularly effective in preventing deficiencies in both mothers and infants. However, vitamin D intake was frequently insufficient in both vegan and omnivorous women, suggesting a need for supplementation across dietary groups. Some studies reported lower birth weights among babies of vegan mothers, though results on small-for-gestational-age prevalence were mixed. Vegan women had lower rates of excessive gestational weight gain, but findings on pre-eclampsia 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.

Journal reference:

• Meulenbroeks D, Otten E, Smeets S, et al. The Association of a Vegan Diet during Pregnancy with Maternal and Child Outcomes: A Systematic Review. Nutrients. (2024), DOI - 10.3390/nu16193329, https://www.mdpi.com/2072-6643/16/19/3329