Over the past decade, new evidence has shown that vitamin D deficiency may 
contribute to the risk of developing a wide range of common chronic diseases 
that are different from the classic action on calcium and bone homeostasis. 
Acting through the vitamin D receptor, vitamin D can produce a wide array of 
favorable biological effects via genomic, non-genomic or intracrine mechanisms 
and, therefore, contributes to the improvement of human health in humans. We 
hypothesize that some of these effects may be even more critical during 
pregnancy. The focus of this paper is to review the data on the classic and 
non-classic actions of vitamin D with regards to pregnancy. It appears that 
vitamin D insufficiency during pregnancy is potentially associated with 
increased risk of preeclampsia, insulin resistance and gestational diabetes 
mellitus. Furthermore, experimental data also anticipate that vitamin D 
sufficiency is critical for fetal development, and especially for fetal brain 
development and immunological functions. Vitamin D deficiency during pregnancy 
may, therefore, not only impair maternal skeletal preservation and fetal 
skeletal formation but also be vital to the fetal "imprinting" that may affect 
chronic disease susceptibility soon after birth as well as later in life.