Research into the extra-skeletal functions of vitamin D has been expanding in recent years. During pregnancy, maternal vitamin D status may be of concern because of the key role of this vitamin in fetal skeletal development and due to the association between hypovitaminosis D and adverse maternal-fetal outcomes. Therefore, the objective of this manuscript was to review the maternal-fetal impact of gestational vitamin D deficiency and the benefits of vitamin D supplementation during pregnancy. A literature search was performed in PubMed and Embase employing the following keywords: vitamin D deficiency, pregnancy, 25-hydroxyvitamin D, and hypovitaminosis D. All relevant articles in English language published since 1980 were analysed by the two authors. Neonatal complications derived from vitamin D deficiency include low birth weight, growth restriction, and respiratory tract infection. In the mother, vitamin D deficiency has been associated with altered glucose homeostasis and increased incidence of gestational diabetes mellitus, pre-eclampsia, and bacterial vaginosis. However, the current state of the evidence is controversial for some other endpoints and the actual benefit of vitamin D supplementation in pregnancy remains unclear. Additional longitudinal studies may clarify the actual impact of vitamin D deficiency during pregnancy, and randomised trials are required to define the benefits of vitamin D supplementation in reducing the incidence of adverse outcomes in the mother and infant.