Researchers studied over 1,400 pregnant women to see if eating a diet focused on plants, whole grains, and less meat and sugar affected their babies’ health. Women who followed this type of diet more closely had babies that were born closer to their due dates and weighed slightly more at birth. Babies born to mothers who ate more saturated fat or added sugar were more likely to be born early and weigh less. The findings suggest that what pregnant women eat might influence when babies are born and how big they are at birth.

The Quick Take

  • What they studied: Whether eating a diet rich in plants, whole grains, nuts, and legumes during pregnancy affects when babies are born and how much they weigh
  • Who participated: 1,431 pregnant women from New Hampshire who were tracked from mid-pregnancy through birth. The study looked at their eating habits around 6 months into pregnancy
  • Key finding: Women who ate more plant-based foods had babies born slightly later (about 3 days longer on average) and weighing about 24 grams more. They also had about 14% lower chances of early birth
  • What it means for you: Eating more plants and fewer processed foods during pregnancy may help babies develop longer in the womb and be born at healthier weights. However, this is one study, and pregnant women should discuss diet changes with their doctor

The Research Details

Researchers followed 1,431 pregnant women from the New Hampshire Birth Cohort Study. At about 6 months into pregnancy, women answered detailed questions about what they ate. The researchers then scored how closely each woman followed a plant-based diet using a special scoring system. After the babies were born, the researchers looked at medical records to find out when each baby was born and how much they weighed, how long they were, and their head size.

The researchers also looked for patterns in eating habits. They found three main types of diets: one focused on plants and whole foods, one with lots of saturated fat (like butter and fatty meats), and one with lots of animal products and added sugars. They then compared birth outcomes between these different eating patterns.

The study controlled for other important factors that affect birth outcomes, like the mother’s age, weight before pregnancy, smoking, and neighborhood income level. This helps show that the diet itself, not these other factors, was connected to the birth outcomes.

This research approach is important because it follows real pregnant women through their actual pregnancies rather than just asking them to remember what they ate after the baby was born. By measuring diet at a specific point in pregnancy (around 6 months), the study captures what women were actually eating during a critical time for baby development. The researchers also looked at specific eating patterns rather than just single foods, which better reflects how people actually eat

This study has several strengths: it included a large number of women (over 1,400), measured diet during pregnancy rather than relying on memory, and adjusted for many other factors that could affect results. However, the study only included women from one state, so results might not apply everywhere. The women who ate more plant-based foods were also older, wealthier, and less likely to smoke, which could have affected the results even though researchers tried to account for this. The study shows associations but cannot prove that diet caused the birth outcomes

What the Results Show

Women who scored highest on the plant-based diet scale had babies that weighed about 24 grams (less than 1 ounce) more at birth compared to those who scored lowest. This might sound small, but even small increases in birth weight are associated with better health outcomes. These women also had pregnancies that lasted about 3 days longer on average, which means their babies had more time to develop in the womb.

Most importantly, women who followed the plant-based diet more closely had about 14% lower chances of giving birth early (before 37 weeks of pregnancy). Early birth is a major health concern because premature babies often need extra medical care and can face health challenges.

When researchers looked at the three different eating patterns, the results were striking. Women who ate a diet high in saturated fat (like butter, fatty meats, and full-fat dairy) had more than 2.5 times higher odds of having a baby with low birth weight. Women who ate lots of animal products and added sugars had babies that weighed about 82 grams (about 3 ounces) less and were slightly shorter.

Both the saturated fat-heavy diet and the animal/added sugar diet were linked to nearly double the odds of early birth. The plant-based eating pattern appeared to be the most protective against these problems. Interestingly, the study found that women who followed the plant-based diet more closely tended to be older, had healthier weights before pregnancy, were less likely to smoke, and lived in wealthier neighborhoods. These factors themselves are known to support healthier pregnancies, so it’s unclear how much of the benefit came from the diet itself versus these other advantages

Previous research has shown that plant-based diets help prevent heart disease, diabetes, and obesity in the general population. This study extends that research by suggesting these diets may also benefit pregnancy outcomes. However, very few studies have looked at how specific diets affect when babies are born and their birth weight, so this research adds important new information. The findings align with general nutrition advice that eating more plants and fewer processed foods is healthier

This study has several important limitations. First, it only included women from New Hampshire, so the results might not apply to women in other regions with different backgrounds or access to foods. Second, women who eat plant-based diets tend to be wealthier and have other health advantages, making it hard to know if the diet itself or these other factors caused the better outcomes. Third, the study only measured diet once during pregnancy, so it doesn’t know if women’s eating changed throughout pregnancy. Fourth, the study cannot prove that diet caused the outcomes—it only shows that certain diets were associated with certain outcomes. Finally, the differences in birth weight, while statistically significant, were quite small in real terms

The Bottom Line

Based on this research, pregnant women may benefit from eating more plant-based foods like vegetables, fruits, whole grains, beans, nuts, and seeds, and eating less saturated fat and added sugar. However, this is one study, and pregnant women should discuss any major diet changes with their doctor or a registered dietitian. The evidence is moderate—the study shows a connection, but more research is needed to be completely certain. Women should not make drastic changes but rather gradually add more plant foods to their diet

This research is most relevant to pregnant women or women planning to become pregnant who want to optimize their nutrition. It’s also important for healthcare providers who advise pregnant women about diet. The findings may be most applicable to women with access to a variety of fresh fruits, vegetables, and whole grains. Women with specific dietary restrictions, allergies, or medical conditions should work with their healthcare provider to adapt these recommendations

If a pregnant woman changes her diet to include more plant-based foods, the benefits would likely begin during the pregnancy itself, as the study measured diet around 6 months into pregnancy. The most significant benefits appear to be preventing early birth and supporting healthy birth weight, which would be evident at the time of delivery. Long-term health benefits for the baby would develop over months and years

Want to Apply This Research?

  • Track daily servings of plant-based foods (vegetables, fruits, whole grains, beans, nuts) and servings of saturated fat sources (fatty meats, butter, full-fat dairy). Aim to increase plant servings and decrease saturated fat servings week by week
  • Start by adding one extra vegetable or fruit serving to each meal, switching to whole grain bread or pasta, and trying one plant-based meal per week. Use the app to log these changes and see progress over time
  • Weekly check-ins on plant food intake and saturated fat reduction. Track mood, energy levels, and any digestive changes. For pregnant users, share progress with healthcare provider at prenatal visits to ensure diet changes are appropriate

This research suggests an association between plant-based eating during pregnancy and better birth outcomes, but it does not prove cause and effect. Pregnant women should not make significant dietary changes without consulting their healthcare provider or a registered dietitian. This information is for educational purposes only and should not replace professional medical advice. Individual pregnancy needs vary, and what works for one person may not work for another. Women with specific health conditions, dietary restrictions, or concerns should work with their healthcare team to develop a personalized nutrition plan