In July 2019 researchers from the USA published their review of the medical scientific literature to assess whether vitamin D supplementation, either alone or in combination with calcium or other vitamins and minerals, given to women during pregnancy can safely improve maternal and neonatal outcomes. A total of 22 studies, involving 3,725 women, were included in the review. Nineteen studies were assessed as having low-to-moderate risk of bias whilst three studies were assessed as having a high risk of bias. Results showed that vitamin D supplementation during pregnancy probably reduced the risk of pre-eclampsia, gestational diabetes as well as reducing the risk of having a baby with a low birthweight (less than 2500 g) (moderate-certainty evidence) compared to women who received placebo or no intervention. However, it was noted that vitamin D supplementation made little or no difference in the risk of having a preterm birth of before 37 weeks compared to no intervention or placebo (low-certainty evidence). In addition, vitamin D supplementation also reduced the risk of severe postpartum haemorrhage (low-certainty evidence). There were also no cases of hypercalcaemia (low-certainty evidence), but it could not be ascertained whether vitamin D increased or decreased the risk of nephritic syndrome (very low-certainty evidence). However, given the scarcity of data in general for maternal adverse events, no firm conclusions could be drawn. Supplementation with vitamin D and calcium during pregnancy was also seen to probably reduce the risk of pre-eclampsia (moderate-certainty evidence) although the evidence was uncertain for gestational diabetes and low birthweight (less than 2500 g) (very low-certainty evidence) compared to women who received placebo. However, supplementation with vitamin D and calcium during pregnancy did appear to increase the risk of preterm birth of before 37 weeks in comparison to women who received placebo or no intervention (low-certainty evidence). Supplementation with vitamin D + calcium + other vitamins and minerals versus calcium + other vitamins and minerals was seen to make little or no difference in the risk of preterm birth of before 37 weeks or low birthweight (less than 2500 g) (low-certainty evidence). However, it was unclear whether it made any difference to the risk of gestational diabetes or maternal adverse events (hypercalcaemia no events or hypercalciuria) as the certainty of the evidence for both outcomes was found to be very low. Further research is required to assess the effects of vitamin D supplementation in pregnancy, particularly in relation to the risk of maternal adverse events.
Palacios C et al. Vitamin D supplementation for women during pregnancy. Cochrane Database Syst Rev. 2019 Jul 26;7:CD008873.