Study: Babies born to vitamin D-deficient mothers more likely to have lower birth weight

PITTSBURGH — Women deficient in vitamin D early in their pregnancies are more likely to deliver babies with lower birth weights, according to research released last week by the University of Pittsburgh Graduate School of Public Health.

The study, funded by the National Institutes of Health, will be reported in the January print edition of the Journal of Clinical Endocrinology & Metabolism.

"A mother's vitamin D level early in pregnancy may impact the growth of her baby later in pregnancy," stated lead author Alison Gernand, post-doctoral associate in Pitt Public Health's Department of Epidemiology. "Also, if the mother was deficient in vitamin D during the first trimester, her baby had twice the risk of suffering from growth restriction in utero."

Gernand and her co-authors discovered that mothers with levels of vitamin D in their blood of less than 0.015 parts per million (37.5 nmol/L) in their first 26 weeks of pregnancy delivered babies who weighed an average of 46 grams less than their peers. Only full-term babies — those delivered between 37 and 42 weeks of pregnancy — were included in the study.

In addition, women who were vitamin D-deficient in the first trimester of pregnancy — 14 weeks or less — were twice as likely to have babies who fell in the lower 10th percentile for weight when compared to other full-term babies born in the same week of pregnancy, a condition known as "small for gestational age."

Babies born small for gestational age are at five to 10 times greater risk for death in their first month and have a higher risk of such chronic diseases as heart disease, hypertension and Type 2 diabetes later in life.

"This is one of the largest studies to examine a mother's vitamin D levels and their relationship with birth weights," noted senior author Lisa M. Bodnar, assistant professor in Pitt Public Health's Department of Epidemiology. "It shows that clinical trials to determine if you can improve birth weights by giving women of reproductive age vitamin D supplements may be warranted."

The Pitt Public Health study used a random sample of 2,146 pregnant women who participated in the Collaborative Perinatal Project, which was conducted in 12 U.S. medical centers from 1959 to 1965. The blood samples collected by the project were well-preserved and able to be tested for vitamin D levels half a century later.

"Although the blood samples were in remarkably good condition, it would be beneficial to repeat our study in a modern sample," Bodnar said. "Today women smoke less, weigh more, have less sun-exposure and get more vitamin D in their foods — all things that could impact their vitamin D levels and babies' birth weights."