The new findings come from US researchers who examined serum vitamin D levels in women expecting babies and analysed them against birth weight outcomes.
"A mother's vitamin D level early in pregnancy may impact the growth of her baby later in pregnancy," said lead author Dr Alison Gernand from the University of Pittsburgh – who led the study.
"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," she said.
Writing in the Journal of Clinical Endocrinology & Metabolism Gernand and her team also reveal 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.
"This is one of the largest studies to examine a mother's vitamin D levels and their relationship with birth weights," said Dr Lisa Bodnar, senior author of the research.
"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," she explained.
The research team included only full-term babies – those delivered between 37 and 42 weeks of pregnancy – from a random sample of 2,146 pregnant women who participated in the Collaborative Perinatal Project, which was conducted in 12 U.S. medical centres 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.
When Gernand and her team tested the samples and analysed them against birth weight outcomes, they found that 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 chronic diseases, such as heart disease, hypertension and type 2 diabetes, later in life.
"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."
Source: Journal of Clinical Endocrinology & Metabolism
Published online ahead of print, doi: 10.1210/jc.2012-3275
“Maternal Serum 25-Hydroxyvitamin D and Measures of Newborn and Placental Weight in a U.S. Multicenter Cohort Study”
Authors: Alison D. Gernand, Hyagriv N. Simhan, Mark A. Klebanoff, Lisa M. Bodnar