Unfortunately, Vitamin D deficiency in pregnancy is an ongoing epidemic, affecting as many as 82% of pregnant women. While studies on Vitamin D supplementation in pregnancy have consistently shown an associated increase in maternal and neonatal serum Vitamin D levels, some studies have also suggested a concurrent decrease in adverse maternal and neonatal outcomes. For example, Vitamin D supplementation in pregnancies with known deficiency has been shown to decrease the incidence of preeclampsia as much as 32%. Other studies, on the other hand, have suggested no benefit. The inconsistency in findings lie in the fact that these studies were primarily observational in nature and plagued by small sample sizes, recall bias, and inability to adjust for potential confounders. Given this, interpretation regarding clinical significance is limited, preventing providers from making appropriate recommendations to their patients. As such, the American Congress of Obstetricians and Gynecologists (ACOG) has called for high quality studies to address whether the use of Vitamin D supplementation beyond that found in prenatal vitamins is beneficial.