The placenta serves as both a barrier and a transporter at the materna
l-fetal interface. Failure of either function leads to fetal compromis
e. Normal placental function requires appropriate early maternal-place
ntal immune interaction in the implantation site; normal uteroplacenta
l perfusion; careful regulation of coagulation pathways; and a healthy
villus trophoblast, stroma, and vasculature. This article discusses b
asic underlying principles.