Study: Vitamin D Status in Early Pregnancy and Infant Outcomes

Vitamin D plays a significant role in the early stages of pregnancy and is essential for immune cell function during implantation and placental formation. Additionally, maternal vitamin D status relates to bone health and formation, fetal skeletal development, and birth weight, according to research published in The American Journal of Clinical Nutrition.^1,2

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Low vitamin D levels are linked with heightened rates of preterm birth and decreased fetal length among women in their first trimester of pregnancy, emphasizing the need for vitamin D monitoring and supplementation in early pregnancy.¹

Despite its essential role in various aspects of pregnancy, vitamin D status in relation to pregnancy outcomes is inadequately understood. To combat this lack of significant data, researchers from the Penn State Department of Nutritional Sciences collaborated with investigators from the University of Utah to assess when vitamin D status is most crucial for optimal fetal growth and pregnancy outcomes, focusing on associations between the first and second trimesters.^1,2

“More than 25% of women who are pregnant or lactating have lower than recommended levels of vitamin D,” Alison Gernand, associate professor of nutritional sciences at Penn State and lead study author, said in a news release. “A lot of the development early in pregnancy requires vitamin D, so we conducted this study to better understand how early-pregnancy vitamin D status is related to pregnancy outcomes.”¹

The longitudinal, observational substudy included blood samples from 351 women collected as part of the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be (nuMoM2b), which employed US pregnant women from 2010 and 2013.^1,2

Vitamin D was measured by nanomoles per liter (nmol/L) of blood, as less than 50 (nmol/L) is considered vitamin D deficient, according to the Institute of Medicine (IOM). The researchers measured 25-hydroxyvitamin D (25(OH)D) among the 351 women at 6 to 13 and 16 to 21 weeks of gestation. Additionally, fetal growth was assessed by ultrasound at 16 to 21 and 22 to 29 weeks of gestation, and neonatal size was measured at birth. The relationship between vitamin D levels and these outcomes, including preterm birth and size for gestational age, was examined using IOM cutoffs (<50 compared with ≥50 nmol/L).^1,2

Among the 351 women included in the study, 20% were vitamin D deficient (25(OH)D <50 nmol/L) in the first trimester. Despite this, the researchers did not find any significant pregnancy outcomes when comparing vitamin D deficient women to vitamin D sufficient women. However, when comparing pregnancy outcomes on a wider range of vitamin D concentrations, the researchers found that pregnant women in their first trimester with vitamin D concentrations lower than 40 nmol/L were 4 times more likely to experience preterm birth compared to women with concentrations greater than or equal to 80 nmol/L. Further first trimester results demonstrated that women with higher levels of vitamin D experienced a .05 [95% confidence interval (CI): .01, .10] increase in fetal length.^1,2

During the second trimester, the researchers did not find a link between maternal vitamin D levels and fetal growth or pregnancy outcomes, possibly due to a high prevalence of healthy vitamin D levels in the study population. However, the study authors noted that further research is needed.^1,2

“This study provides evidence that early pregnancy—and even preconception—nutrition is vitally important,” Celeste Beck, associate research scientist lead at Heluna Health and lead study author, said in a news release. “Individual women may or may not need supplements depending on their diet and lifestyle. But healthy nutrition is critical for promoting the healthy development of a fetus. This research indicates that vitamin D levels—along with iron, folate, and other essential nutrients in pregnancy—should be monitored and understood by obstetricians and women early on to promote healthy birth outcomes.”¹

Pharmacists can suggest vitamin D-dense foods like salmon, herring, and sardines; cod liver oil; canned tuna; egg yolks; and mushrooms to pregnant women that are not receiving enough vitamin D in their natural diet. Additionally, other vitamin D-fortified foods like cow’s milk, soy milk, orange juice, and cereal and oatmeal can be recommended for women that are vegetarian or do not like fish.³

“We can't just assume that everybody is deficient, but proper nutrition is something that needs to be on your radar if you may become pregnant," Gernand said. “And this study provides evidence that vitamin D appears to be an important part of a pregnant woman’s nutritional health.”¹

REFERENCES

1. Vitamin D matters during first trimester, researchers find. Eurek Alert!. News release. Published February 3, 2025. Accessed February 10, 2025. https://www.eurekalert.org/news-releases/1072441

2. Maternal vitamin D status, fetal growth patterns, and adverse pregnancy outcomes in a multisite prospective pregnancy cohort. The American Journal of Clinical Nutrition. News release. Published February 2025. Accessed February 10, 2025. https://www.sciencedirect.com/science/article/pii/S0002916524008906

3. 7 Nutritious Foods That Are High in Vitamin D. Healthline. News release. Updated July 6, 2023. Accessed February 10, 2025. https://www.healthline.com/nutrition/9-foods-high-in-vitamin-d#summary