CYP27B1 and Stillbirth: Regarding mechanistic exploration, rodent models (e.g., mice) of maternal VD deficiency can be constructed by dietary restriction (VD-deficient diet) or specific gene knockout (Cyp27b1+/−) to observe the effects of maternal VD deficiency on adverse pregnancy outcomes (GDM, PIH, spontaneous abortion, stillbirth, PTB, and IUGR).