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A recent study has found that maternal vitamin D levels in the first trimester of pregnancy play a significant role in fetal growth and the risk of preterm birth. The research highlights that pregnant individuals with serum 25-hydroxyvitamin D (25(OH)D) concentrations below 40 nmol/L have a 4.35 times higher likelihood of preterm birth. Furthermore, higher levels of 25(OH)D during the first trimester positively correlate with fetal linear growth patterns.
Study Methodology
The study was a secondary analysis of data from a multisite prospective cohort study involving 351 nulliparous pregnant women in the United States. Researchers measured serum 25(OH)D levels at two time points—6-13 weeks and 16-21 weeks of gestation. They also conducted fetal growth assessments using ultrasound at 16-21 weeks and 22-29 weeks, in addition to measuring neonatal anthropometric indicators at birth. Fetal growth curves were constructed based on length, weight, and head circumference z-scores.
Participants were randomly selected to ensure representation of the original cohort distribution, which included 16% with adverse pregnancy outcomes and 84% without. Inclusion criteria required participants to be at least 18 years old and have a body mass index (BMI) of at least 18.5.
Key Findings
- For every 10 nmol/L increase in first trimester 25(OH)D levels, there was a 0.05 increase (95% CI, 0.01-0.10) in length-for-age z-score.
- Participants with first trimester 25(OH)D levels below 40 nmol/L had a significantly higher risk of preterm birth (odds ratio: 4.35; 95% CI, 1.14-16.55) compared to those with levels exceeding 80 nmol/L.
- Vitamin D insufficiency was present in 20% of the participants, with a mean 25(OH)D concentration of 68.1 nmol/L (SD: 21.0).
- Second trimester 25(OH)D levels did not show any significant associations with fetal growth patterns or pregnancy outcomes.
Clinical Implications
The study suggests that early pregnancy, or even preconception, may represent a critical window for vitamin D intervention in individuals with deficiency. “These findings were observed in a study population where 80% of pregnant females met vitamin D sufficiency criteria in the first trimester. Few studies have examined fetal growth patterns in relation to early pregnancy maternal vitamin D status, and ours is the first study we are aware of to examine multiple time points of early pregnancy maternal 25(OH)D in association with fetal growth,” the study authors stated.
Study Limitations
The authors noted certain limitations, including a relatively small sample size and a low number of participants with severe vitamin D deficiency (<30 nmol/L). These constraints limited their ability to compare fetal growth and birth outcomes among participants with extremely low vitamin D levels. Additionally, the small number of cases of small-for-gestational-age births and preterm births restricted the statistical adjustments possible for certain covariates.
Funding and Disclosures
This study was supported by the US Department of Health and Human Services, the National Institutes of Health, and the Eunice Kennedy Shriver National Institute of Child Health and Human Development. The authors reported no conflicts of interest.
Disclaimer
This article is for informational purposes only and does not constitute medical advice. Pregnant individuals or those planning pregnancy should consult their healthcare provider for personalized guidance on vitamin D supplementation and prenatal care.
Source: Beck C, et al. “First Trimester Vitamin D Status and Fetal Growth.” The American Journal of Clinical Nutrition. Published online.
