Vitamin D supplementation for women during pregnancy

Vitamin D deficiency or insufficiency is thought to be common among pregnant women. Vitamin D supplementation during pregnancy has been suggested as an intervention to protect against adverse gestational outcomes. To examine whether supplements with vitamin D alone or in combination with calcium or other vitamins and minerals given to women during pregnancy can safely improve maternal and neonatal outcomes. We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 October 2011), the International Clinical Trials Registry Platform (ICTRP) (31 October 2011), the Networked Digital Library of Theses and Dissertations (28 October 2011) and also contacted relevant organisations (8 April 2011). Randomised and quasi-randomised trials with randomisation at either individual or cluster level, evaluating the effect of supplementation with vitamin D alone or in combination with other micronutrients for women during pregnancy. Two review authors independently i) assessed the eligibility of studies against the inclusion criteria ii) extracted data from included studies, and iii) assessed the risk of bias of the included studies. Data were checked for accuracy. The search strategy identified 34 potentially eligible references. We included six trials assessing a total of 1023 women, excluded eight studies, and 10 studies are still ongoing. Five trials involving 623 women compared the effects of vitamin D alone versus no supplementation/placebo and one trial with 400 women compared the effects of vitamin D and calcium versus no supplementation.Only one trial with 400 women reported on pre-eclampsia: women who received 1200 IU vitamin D along with 375 mg of elemental calcium per day were as likely to develop pre-eclampsia as women who received no supplementation (average risk ratio (RR) 0.67; 95% confidence interval (CI) 0.33 to 1.35). Data from four trials involving 414 women consistently show that women who received vitamin D supplements had higher concentrations of vitamin D in serum at term than those women who received no intervention or a placebo; however the magnitude of the response was highly heterogenous. Data from three trials involving 463 women suggest that women who receive vitamin D supplements during pregnancy less frequently had a baby with a birthweight below 2500 grams than those women receiving no treatment or placebo; statistical significance was borderline (RR 0.48; 95% CI 0.23 to 1.01).In terms of other conditions, there were no si