This umbrella review summarizes systematic reviews and meta-analyses evaluating the effects of vitamin D deficiency and supplementation during pregnancy on maternal and offspring health. Vitamin D deficiency was associated with increased risks of preterm birth, small-for-gestational-age/low birth weight infants, recurrent miscarriage, bacterial vaginosis, and gestational diabetes mellitus (GDM). Supplementation increased birth weight and reduced risks of maternal pre-eclampsia, miscarriage, vitamin D deficiency, fetal/neonatal mortality, childhood attention-deficit hyperactivity disorder, and autism spectrum disorder. In women with GDM, supplementation reduced risks of maternal hyperbilirubinemia, polyhydramnios, macrosomia, fetal distress, and neonatal hospitalization. Monitoring vitamin D status and supplementation of >400 IU/day are recommended.
