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First Trimester Vitamin D Levels May Impact Pregnancy Outcomes

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Vitamin D plays an important role in our bodies, promoting bone and muscle health, among other functions.


In pregnancy, vitamin D is associated with the production of pro-angiogenic factors that support the development of the placenta. Maternal vitamin D status has also been linked to fetal development and birth weight.


What lacks in this research area, however, is an understanding of whether vitamin D levels across the gestational period are associated with specific fetal growth patterns and pregnancy outcomes. Most studies have analyzed data from women mid-gestation; very few studies have explored vitamin D levels between the first and second trimesters.


Consequently, there is an information gap. Researchers led by Dr. Alison Gernand, associate professor of nutritional sciences at Penn State University, sought to fill it using study data and samples from the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be (nuMoM2b).


What is nuMoM2B?

nuMoM2b is a prospective cohort study of 10,038 pregnant women who are delivering for the first time. Beginning in 2010, the study enrolled pregnant women from diverse ethnic groups across 8 clinical research sites and 12 subsites in the United States.

Vitamin D and pregnancy outcomes assessed

Gernand and colleagues randomly selected a sample of 351 participants from the nuMoM2b cohort who were, on average, 27.9 years of age with a BMI of 26.6 kg/m2.


Participants’ blood samples were analyzed for serum 25-hydroxyvitamin – or 25(OH)D – concentrations at 6–13 and 16–21 weeks of gestation using liquid chromatography-mass spectrometry.


What is 25-hydroxyvitamin, or 25(OH)D?

25(OH)D is the major circulating form of vitamin D and is therefore considered the gold-standard measure of vitamin D intake from UV radiation and food.


Participants also underwent ultrasound scans at 16–21 weeks and 22–29 weeks of gestation, with neonatal anthropometric measures collected at birth.

“We constructed fetal growth curves using length, weight and head circumference z-scores, and calculated risk of preterm birth (<37 weeks) and small for gestational age,” the researchers explained.

Gernand and team examined pregnancy outcomes across serum 25(OH)D concentrations using the Institute of Medicine cutoffs, which state that 25(OH)D concentrations of <30 nmol/L represent vitamin D deficiency, <50 nmol/L represent insufficiency and ≥50 nmol/L represent sufficiency, in addition to exploratory cutoffs.

Women with low vitamin D levels in first trimester more likely to experience pre-term birth

No statistical differences in pregnancy outcomes were identified between women with vitamin D insufficiency and vitamin D sufficiency.


When Gernand and team analyzed the data from a wider range of concentrations, though, the results changed.


Women in their first trimester with 25(OH)D concentrations less than 40 nmol/L were 4.35 times more likely to have a preterm birth compared to women with 25(OH)D concentrations ≥80 nmol/L.


As only 29 infants (8%) were born preterm in the study cohort, the researchers emphasize that additional studies in larger cohorts are warranted. It’s also important to note that correlation or association does not necessarily mean causation.

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A statistically significant association was also observed between 25(OH)D concentrations in the first trimester and fetal growth patterns. “When we examined first trimester 25(OH)D continuously in relation to longitudinal fetal growth patterns, we observed associations between 25(OH)D and linear growth, but not with weight or head circumference in adjusted models,” Gernand and colleagues explained.


This association was not observed in data from the second trimester. However, 74% of participants showed an increase in 25(OH)D levels between their first and second trimesters, which may have impacted the researchers’ ability to detect an association.

Vitamin D important for pregnancy health

These data emphasize the importance of early pregnancy and even pre-conception nutrition, according to Dr. Celeste Beck, the study’s first author and a former doctoral student in nutritional sciences at Penn State: “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.”


“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 added. “And this study provides evidence that vitamin D appears to be an important part of a pregnant woman’s nutritional health.”


Future research should aim to clarify the role that timing of vitamin D supplementation might have with regard to pregnancy outcomes.


This article is a rework of a press release issued by Penn State University. Material has been edited for length and content.


Reference: Beck C, Blue NR, Silver RM, et al. Maternal vitamin D status, fetal growth patterns, and adverse pregnancy outcomes in a multisite prospective pregnancy cohort. AJCN. 2025;121(2):376-384. doi: 10.1016/j.ajcnut.2024.11.018