During the two-year study, Boston University School of Medicine and Boston Medical Center researchers examined the relationship between vitamin D levels in pregnant women and Caesarean section. Of the 253 women in the study, 43 (17 percent) had a Caesarean section.

The study found that 28 percent of women with serum 25-hydroxyvitamin D [25 (OH) D] less than 37.5 nmol/L had a Caesarean section, compared to 14 percent of women with 25 (OH) D greater than 37.5 nmol/L.

"In our analysis, pregnant women who were vitamin D-deficient at the time of delivery had almost four time the odds of Caesarean birth than women who were not deficient," study author Dr. Michael Holick, director of the General Clinical Research Center, a professor of medicine, physiology and biophysics, and an assistant professor of medicine, said in a medical center news release.

He noted that previous research has linked vitamin D deficiency with proximal muscle weakness and suboptimal muscle performance and strength, which may help explain the findings.

The study was published online in The Journal of Clinical Endocrinology & Metabolism.