Summary:
The aim of this study was to assess whether a mother’s vitamin D levels in the first and second trimesters are linked to fetal growth and health outcomes. Data were taken from a large study in the U.S. that followed first-time pregnant women. The researchers looked at the vitamin D levels of 351 participants at two stages: 6-13 weeks and 16-21 weeks of pregnancy. Fetal growth was then measured by checking ultrasounds at 16-21 and 22-29 weeks, as well as birth weight. The results showed that 20% of participants had insufficient vitamin D levels in the first trimester. For every 10 nmol/L increase in vitamin D during the first trimester, the baby’s length increased by 0.05. There were no significant differences in the risk of preterm birth or being small for gestational age; however, women with vitamin D levels below 40 nmol/L in the first trimester had a 4.35 times higher risk of preterm birth compared to those with levels above 80 nmol/L. In contrast, second trimester vitamin D levels didn’t seem to affect fetal growth or pregnancy outcomes. In conclusion, having higher vitamin D levels in the first trimester is linked to better linear growth in the baby. Very low vitamin D levels in the first trimester are associated with a higher risk of preterm birth.
Abstract:
Background: Few studies have examined maternal vitamin D status and fetal growth patterns across gestation. Furthermore, time points in pregnancy at which maternal vitamin D status is most critical for optimal fetal growth and pregnancy outcomes are uncertain. Objectives: Our objective was to examine whether first and second trimester maternal vitamin D status are associated with fetal growth patterns and pregnancy outcomes. Methods: We conducted a secondary analysis using data and samples from a multisite prospective cohort study of nulliparous pregnant females in the United States. We measured serum 25-hydroxyvitamin D (25(OH)D) for 351 participants at 6–13 and 16–21 weeks of gestation. Fetal growth was measured by ultrasound at 16–21 and 22–29 weeks of gestation, and neonatal anthropometric measures at birth. We constructed fetal growth curves using length, weight, and head circumference z-scores, and calculated risk of preterm birth (<37 wk) and small for gestational age (SGA). We examined outcomes across 25(OH)D concentrations assessed continuously, using Institute of Medicine (IOM) cutoffs (<50 compared with ≥50 nmol/L), and using exploratory cutoffs (<40, 40–59.9, 60–79.9, ≥80 nmol/L). Results: Vitamin D insufficiency (25(OH)D <50 nmol/L) was prevalent in 20% of participants in the first trimester. Each 10 nmol/L increase in first trimester 25(OH)D was associated with a 0.05 [95% confidence interval (CI): 0.01, 0.10] increase in length-for-age z-score but was not associated with weight or head circumference. There were no differences in risk of preterm birth or SGA using IOM cutoffs; participants with first trimester 25(OH)D <40 compared with ≥80 nmol/L had 4.35 (95% CI: 1.14, 16.55) times risk of preterm birth. Second trimester 25(OH)D was not associated with fetal growth patterns or with pregnancy outcomes. Conclusions: First trimester 25(OH)D is positively associated with linear growth. Low first trimester 25(OH)D (<40 nmol/L) is associated with a higher risk of preterm birth. Second trimester 25(OH)D is not associated with fetal growth or pregnancy outcomes assessed.
Article Publication Date: 03/02/2025
DOI: 10.1016/j.ajcnut.2024.11.018
