A NEW study has found that maternal vitamin D levels in early pregnancy may play a crucial role in fetal growth and the risk of preterm birth. The research, conducted as a secondary analysis of a multisite prospective cohort study in the United States, highlights the importance of adequate vitamin D levels during the first trimester of pregnancy.
The study examined data from 351 nulliparous pregnant females, measuring serum 25-hydroxyvitamin D (25(OH)D) levels at 6–13 and 16–21 weeks of gestation. Fetal growth was assessed via ultrasound at 16–21 and 22–29 weeks, while neonatal measurements were taken at birth. The researchers aimed to determine whether maternal vitamin D levels in the first and second trimesters were associated with fetal growth patterns and pregnancy outcomes.
Findings revealed that 20% of participants had vitamin D insufficiency (<50 nmol/L) during the first trimester. A 10 nmol/L increase in first trimester 25(OH)D was linked to a 0.05 increase in length-for-age z-score, indicating a positive association with linear fetal growth. However, no significant correlations were found between vitamin D levels and fetal weight or head circumference.
Notably, participants with first trimester vitamin D levels below 40 nmol/L faced a significantly increased risk of preterm birth, with a 4.35 times greater likelihood compared to those with levels of 80 nmol/L or higher. Despite this association, the study found no significant differences in the risk of preterm birth or small-for-gestational-age (SGA) status when using standard Institute of Medicine (IOM) cutoffs (<50 vs. ≥50 nmol/L). Additionally, vitamin D levels in the second trimester were not associated with fetal growth patterns or pregnancy outcomes.
These findings suggest that adequate vitamin D levels in early pregnancy may be essential for optimal fetal development and reducing the risk of preterm birth. The study underscores the need for further research into maternal vitamin D supplementation and its potential benefits for pregnancy outcomes.
Reference
Beck C et al. Maternal vitamin D status, fetal growth patterns, and adverse pregnancy outcomes in a multisite prospective pregnancy cohort. Am J Clin Nutr. 2025;121(2):376-84.
