Last reviewed 04/2023

Placentation is the growth and formation of the placenta and the development of the uterine capacity to supply the blood required. Thus the spiral arteries, which normally carry 5 ml of blood per minute carry some 500 ml per minute at term.

An important process taking place is the remodelling of the spiral arteries into widely dilated conduits for exchange This is effected by fetal cells which invade the endometrium, migrate to the lumen of the spiral arteries, where breakdown and remodelling takes place, such that the arteries take on a non-muscular, fibrinoid structure.

This invasion occurs with cells at the decidual / myometrial at 12 weeks, continuing until 18 weeks when it becomes quiescent. The cells are almost all gone at term.

Placentation is frequently abnormal in pre-eclampsia.