Maternal vitamin A and D levels don’t predict birth weight in pregnant women with overweight or obesity, according to a 2026 study of 57 mothers published in Frontiers in Endocrinology. While vitamin A and D declined during pregnancy and vitamin E increased, these changes showed no connection to whether babies were born at normal weight or larger than average. Gram Research analysis suggests that other factors beyond these three fat-soluble vitamins may be more important for controlling fetal growth in metabolically high-risk pregnancies.
A new study looked at whether vitamins A, D, and E during pregnancy affect how much babies weigh at birth. Researchers tracked 57 pregnant women who were overweight or obese, measuring their vitamin levels in the second and third trimesters. They found that while many mothers had low vitamin levels—and nearly half their babies were born larger than average—the vitamin levels didn’t actually predict birth weight. This suggests that for pregnant women with weight challenges, other factors may be more important in determining how big babies grow.
Key Statistics
A 2026 study of 57 pregnant women with overweight or obesity found that vitamin A levels dropped 13% from the second to third trimester, declining from 1.52 to 1.32 µmol/L, yet this decline showed no association with infant birth weight.
In the same 2026 research of 57 mother-infant pairs, 44% of babies were born with macrosomia (weighing over 8.8 pounds), yet maternal vitamin A, D, and E levels failed to predict which infants would be larger than average.
A 2026 analysis found that by the third trimester, 31.6% of pregnant women with overweight or obesity had vitamin D deficiency and 33.3% had insufficiency, but these deficiencies were not independently associated with birth weight outcomes.
Vitamin E levels increased 34% during pregnancy in the 2026 study (from 34.6 to 46.3 µmol/L), while vitamin A and D declined, yet none of these vitamin trajectories predicted infant birth weight in women with pre-pregnancy overweight or obesity.
The Quick Take
- What they studied: Whether the amounts of vitamins A, D, and E in a pregnant mother’s blood affect how much her baby weighs when born
- Who participated: 57 pregnant women who were overweight or obese, with measurements taken during months 4-6 and months 7-9 of pregnancy
- Key finding: Vitamin A and D levels dropped during pregnancy, vitamin E went up, but none of these changes predicted whether babies would be born at normal weight or larger than average
- What it means for you: If you’re pregnant and overweight, focusing only on these three vitamins may not be the key to controlling your baby’s birth weight. Talk to your doctor about what factors actually matter most for your situation.
The Research Details
This was a secondary analysis, meaning researchers used data already collected from a larger pregnancy exercise study called ETIP. They looked back at 57 mother-baby pairs who had vitamin measurements taken twice during pregnancy—once in the middle (second trimester) and once near the end (third trimester). The researchers measured three fat-soluble vitamins (A, D, and E) using specialized laboratory techniques that can detect tiny amounts of these nutrients in blood samples. They then compared these vitamin levels to the babies’ birth weights, categorizing babies as either normal weight (5.5-8.8 pounds) or macrosomic, which means unusually large (over 8.8 pounds).
This approach is important because it looks at real pregnancy data from women who face metabolic challenges due to their weight. Rather than just measuring vitamins once, the researchers tracked changes across pregnancy, which gives a better picture of how vitamin levels shift during this critical time. By examining actual birth outcomes, they could see whether these vitamin changes actually matter for fetal growth.
The study is relatively small (57 participants), which means the findings are preliminary and need confirmation in larger groups. However, the researchers used precise laboratory methods to measure vitamins, and they carefully tracked mothers across two time points in pregnancy. The study was published in a peer-reviewed journal, meaning other experts reviewed the work. The main limitation is that this was a secondary analysis, so the original study wasn’t designed specifically to answer this vitamin question.
What the Results Show
The researchers found clear patterns in how vitamin levels changed during pregnancy. Vitamin A dropped by about 13%, falling from an average of 1.52 to 1.32 units. Vitamin D also declined significantly, dropping from 73.7 to 63.3 units—a decrease of about 14%. In contrast, vitamin E actually increased by about 34%, rising from 34.6 to 46.3 units. By the third trimester, vitamin deficiencies were common: about 1 in 5 mothers had insufficient vitamin A, nearly 1 in 3 had vitamin D deficiency, and another third had vitamin D insufficiency. Despite these widespread vitamin shortages, the vitamin levels showed no connection to birth weight. Babies born to mothers with low vitamins weighed about the same as babies born to mothers with adequate vitamins.
Macrosomia (larger-than-average birth weight) was very common in this group, occurring in 44% of babies. This high rate reflects the metabolic challenges that overweight and obese pregnant women face. However, the vitamin levels didn’t explain why some babies were larger. The researchers also checked whether vitamins A and D worked together to affect birth weight, but found no interaction between them either.
Previous research suggested that fat-soluble vitamins might influence fetal growth because they affect important biological pathways. However, this study suggests that in pregnant women with overweight or obesity, these vitamins may play a smaller role than expected. The findings align with emerging evidence that metabolic factors beyond single nutrients may be more important for determining birth weight in this population.
The study included only 57 women, which is a small sample size. Larger studies would provide more reliable answers. The research focused only on women with overweight or obesity, so results may not apply to women of normal weight. The study measured vitamins only twice during pregnancy, so researchers couldn’t track changes throughout all nine months. Additionally, the original study wasn’t designed to examine vitamins, so some relevant information may not have been collected.
The Bottom Line
According to Gram Research analysis, pregnant women with overweight or obesity should still maintain adequate vitamin intake as part of general prenatal care, but these three fat-soluble vitamins alone are unlikely to be the main factor controlling birth weight. Work with your healthcare provider on a comprehensive approach that may include weight management, physical activity, and overall nutrition rather than focusing narrowly on vitamins A, D, and E. Confidence level: Moderate—this finding needs confirmation in larger studies.
This research is most relevant to pregnant women who are overweight or obese, their doctors, and prenatal care providers. Women of normal weight may have different vitamin-birth weight relationships. Healthcare providers managing gestational diabetes or other metabolic complications should consider that vitamin status may not be the primary driver of fetal growth in their patients.
Birth weight is determined during pregnancy and cannot be changed after birth. If you’re planning pregnancy or currently pregnant, optimizing vitamin levels now is important for overall health, but don’t expect vitamin supplementation alone to dramatically change your baby’s birth weight.
Frequently Asked Questions
Does taking vitamin D during pregnancy help control baby’s birth weight?
A 2026 study of 57 pregnant women with overweight or obesity found that vitamin D levels didn’t predict birth weight, even though 65% had vitamin D deficiency or insufficiency. Other factors appear more important for controlling fetal growth in this population.
What vitamins should I take if I’m overweight and pregnant?
Continue taking prenatal vitamins as recommended by your doctor, but understand that vitamins A, D, and E alone won’t determine your baby’s size. Focus on comprehensive prenatal care including nutrition quality, physical activity, and weight management for better outcomes.
Why do overweight pregnant women have larger babies?
A 2026 study found 44% of babies born to overweight mothers had macrosomia, but vitamin levels didn’t explain this. The connection likely involves broader metabolic factors like insulin resistance and glucose control rather than single nutrients.
Can I prevent a large baby by taking more vitamins?
Research shows vitamin supplementation alone won’t prevent macrosomia in overweight pregnancies. Work with your healthcare provider on comprehensive strategies including weight management, physical activity, and blood sugar control.
What should I monitor during pregnancy if I’m overweight?
Beyond standard prenatal care, track weight gain patterns, blood sugar levels, physical activity, and overall nutrition quality. These factors appear more influential than individual vitamin levels for controlling fetal growth in metabolically high-risk pregnancies.
Want to Apply This Research?
- Log prenatal vitamin intake daily and track trimester-specific vitamin D and A levels from lab work (if available). Note any changes in supplement dosing and correlate with weight gain patterns and provider feedback on fetal growth measurements.
- Set reminders to take prenatal vitamins consistently, but also focus the app on tracking overall nutrition quality, physical activity, and weight gain patterns—factors that may matter more for birth weight than individual vitamin levels.
- Use the app to monitor comprehensive prenatal health metrics: daily vitamin adherence, weekly weight trends, exercise minutes, and ultrasound measurements of fetal growth. Share this data with your healthcare provider to identify patterns beyond just vitamin status.
This research is preliminary and based on a small sample of 57 pregnant women. The findings apply specifically to pregnant individuals with overweight or obesity and may not generalize to other populations. Vitamin supplementation remains important for overall prenatal health and should not be discontinued without consulting your healthcare provider. Birth weight is influenced by multiple factors beyond vitamin status. Always discuss pregnancy nutrition and supplementation decisions with your obstetrician or midwife, who can provide personalized recommendations based on your individual health status and medical history. This article is for educational purposes and should not replace professional medical advice.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.