Sunlight Benefits for the Womb

Vitamin D levels in pregnant women appear linked to birthweight of newborns

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) Being born underweight is linked to a variety of possible health problems, including chronic diseases. It's therefore helpful to know ways to reduce the risk of having too-small babies.

A recent studied looked at whether a mother's vitamin D levels might play a part in her baby's weight at birth.

The researchers found that a certain threshold exists for vitamin D levels in pregnant women, especially during the first trimester.

If women had levels of at least 37.5 nmol/liter of vitamin D, there appeared to be no link to their babies' birthweight.

Women who had lower levels than this were more likely to have had an underweight baby, in proportion to how much vitamin D they had.

"Take prenatal vitamins while pregnant."

The study, led by Alison D. Gernand, PhD, MPH, of the Department of Epidemiology at the University of Pittsburgh Graduate School of Public Health, looked at the link between vitamin D levels in pregnant women and their babies' birthweight.

The study included 2,146 women whose vitamin D levels were measured when they were no more than 26 weeks pregnant.

When the women gave birth, the researchers gathered information on the babies' birthweight, the weight of the women's placentas and whether the babies were a healthy weight for their age.

The researchers adjusted their analysis to take into account the women's race/ethnicity, age, pre-pregnancy weight, height, number of children, smoking status, marital status and income.

They also took into account the sex of the baby, the pregnancy week when the women's vitamin D levels were tested and the time of year (since vitamin D levels are higher with more sunlight exposure).

The researchers found that women who had at least 37.5 nmol/liter of vitamin D gave birth to newborns that were an average 1.6 ounces heavier than the newborns of mothers with lower vitamin D levels.

The women with more vitamin D also had babies' with 0.13 cm larger head circumferences, as compared to the babies of moms with lower vitamin D levels.

Among the women with vitamin D levels below 37.5 nmol/liter, the weight of their newborns and the circumferences of their newborns' heads increased as the mothers' vitamin D levels increased. After 37.5 nmol/liter, the differences leveled off.

The mothers with at least 37.5 nmol/liter of vitamin D during their first trimester were also half as likely to have a baby that was small for its age, or underweight at birth.

However, mothers' vitamin D levels during their second trimester did not seem linked to whether newborns were a healthy weight at birth.

The researchers determined that vitamin D levels in mothers do appear related to how babies are growing in the womb. They recommended further research to understand whether women should take additional vitamin D.

Pregnant women should not start vitamin D or any other vitamin supplementation without first discussing it with their prenatal care physician.

The study was published online in November in the Journal of Clinical Endocrinology & Metabolism and will appear in an upcoming print issue. The research was funded by the National Institutes of Health. The authors declared no conflicts of interest.

Reviewed by: 
Review Date: 
February 10, 2013
Last Updated:
February 12, 2013