Regarding, trophoblast invasion of maternal spiral arteries, all are true except
Trophoblastic invasion involves only decidual spiral arteries.
First wave occurs before 12 weeks and consists of invasion upto border between decidua and myometrium.
Second wave occurs between 12 and 16 weeks with invasion of intramyometrial segments of spiral arteries.
Narrow lumen, muscular spiral arteries are converted into dilated, low resistance vessels.
Invasion by trophoblasts involves both decidual spiral arteries and decidual veins.