Effects of Vitamin D Supplementation During Pregnancy on Birth Size: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.

Plain Language Summary

Vitamin D deficiency may affect mother and neonatal outcomes, increasing the risk of pregnancy complications, preterm birth, low birth weight (LBW), small for gestational age (SGA), and poor offspring health. This systematic review and meta-analysis evaluates the effects of oral vitamin D supplementation during pregnancy on foetal growth and incidence of LBW and SGA births. 13 randomised controlled trials (RCTs), published between 1980 and 2016, were included in the meta-analysis, including in total 2016 newborns (1184 from mothers in the intervention groups and 832 from controls). Dosages ranged from 200-4000 IU for daily intakes and 35000 IU to 600000 IU for single or intermittent administration. Whilst there was no evidence for publication bias (e.g. an over-reporting of positive outcomes), overall, the quality of the reviewed studies varied from very low (head circumference) to moderate (birth weight, birth length, LBW, and SGA). All studies evaluating the effect of vitamin D supplementation on blood 25-hydroxyvitamin D (OHD) levels showed that intervention significantly increased 25-OHD concentration in both mothers and infants. The meta-analysis showed that vitamin D supplementation significantly increased birth weight and length, independent of dosage and whether vitamin D was administered daily or in single/intermittent high dosages. Head circumference was increased in a non-dose dependent way with daily but not with single/intermittent vitamin D supplementation. Effects on all three parameters were seen when vitamin D was supplemented alone, but not in combination with other nutrients. Both, risk of LBW and SGA, were also significantly reduced with vitamin D supplementation.