Andrée Gruslin award lecture: Vitamin D, pregnancy and the human placenta.

Vitamin D plays diverse and complex roles during pregnancy affecting the mother, placenta and fetus. Vitamin D affects calcium homeostasis, cell proliferation and differentiation, inflammation and immune function. Understanding the roles of vitamin D in pregnancy is hindered by the complexity of vitamin D metabolism that generates multiple metabolites, transfer and processing by the placenta, and uncertainty of whether the biological effects are mediated directly in fetal organs or indirectly through the placenta. It is therefore necessary to distinguish the effects of vitamin D on the placenta from those of vitamin D transferred to the fetus by the placenta. The current understanding of the physiology of vitamin D during human pregnancy, specifically its interaction with the placenta will be discussed in this review. The evidence base linking placental function to fetal vitamin D supply will be discussed in relation to the underlying mechanisms, along with the placental responses to maternal vitamin D levels and their influence on fetal development. A greater understanding of pregnancy-specific vitamin D physiology is key to addressing clinical complications linked to impaired vitamin D status during pregnancy and designing effective interventions.