1. Maternal serum vitamin D levels ≤ 20 weeks gestation were inversely associated with incidence of preterm birth.
2. A similar inverse relationship was seen in spontaneous, medically indicated and very preterm (<34 week gestation) births.
Evidence Rating Level: 3 (Average)
Study Rundown: Preterm birth is a leading cause of neonatal mortality worldwide and has even been associated with long-term health problems for the mother. While the cause of preterm birth is likely multifactorial, there is increasing evidence that intrauterine infection during pregnancy is an important and common cause. Vitamin D has been shown to act as a natural antibiotic, by inducing bacteria-fighting proteins in the placenta. The normal range for serum 25-hydroxyvitamin D, an easily measured metabolite, is 50-80 nmol/L for a healthy adult, although these norms vary slightly by source. Studies have shown an association between maternal vitamin D levels and placental antibacterial response. However, mixed findings have been seen among studies examining vitamin D supplementation and preterm birth. In this study, researchers attempted to address these discrepancies by looking at the association between maternal vitamin D levels and the frequency of preterm birth.
Researchers found that maternal vitamin D levels were inversely associated with incidence of preterm birth in a dose-dependent manner. Limitations of this study included the observational study design and study of high-risk pregnancies such that results may not be readily extrapolated to the general population. Further, 25-hydroxyvitamin D may not be an accurate proxy for vitamin D activity in the body. A randomized controlled trial of vitamin D supplementation compared with placebo in women who are vitamin D-deficient would further support these findings.
Click to read the study in Obstetrics & Gynecology
Relevant Reading: Health characteristics and outcomes of two randomized vitamin D supplementation trials during pregnancy
Study Author, Dr. Lisa M. Bodnar, PhD, RD, talks to 2 Minute Medicine: University of Pittsburgh, Department of Epidemiology, Graduate School of Public Health
“Our study suggests that vitamin D deficiency in the first half of pregnancy may contribute to preterm birth, even after holding other risk factors such as race and smoking constant. Health care providers should continue to follow the current guidelines on vitamin D supplementation, which include recommending that women take a prenatal vitamin that contains vitamin D.”
In-Depth [case-cohort study]: Researchers randomly selected 2327 deliveries to serve as a sub-cohort and all remaining preterm births (n=1126) to serve as cases from a larger cohort of women at one academic center who had stored prenatal aneuploidy screening serum samples from 20 weeks or prior and went on to deliver a live, singleton neonate. Maternal serum 25-hydroxyvitamin D levels were measured in the stored samples. Multivariate models were used to look for an association between maternal vitamin D status and preterm birth at both <37 weeks gestation and <34 weeks gestation.
In women with a serum vitamin D of <50 nmol/L, the incidence of preterm at <37 weeks was 11.3% compared to an incidence of 7.3% in women with serum levels ≥75 nmol/L (p<0.05 for all). After controlling for known confounders, including maternal race, BMI, season, and smoking status, the incidence of preterm birth decreased as vitamin D levels increased up to 90nmol/L, where they plateaued. Results were similar in other subtypes of preterm birth, including medically indicated, spontaneous, and those at <34 weeks gestation.
More from this author: Vitamin D deficiency linked with decreased pregnancy rates in IVF, C-section in the second stage linked to future preterm birth, Phthalate exposure during pregnancy associated with preterm birth, Better preterm outcomes after vaginal delivery, Prenatal inflammatory markers associated with adverse neonatal outcomes
Image: PD
©2014 2 Minute Medicine, Inc. All rights reserved. No works may be reproduced without expressed written consent from 2 Minute Medicine, Inc. No article should be construed as medical advice and is not intended as such by the authors, editors, staff or by 2 Minute Medicine, Inc.
