Gynaecology & Obstetrics Regarding, trophoblast invasion of maternal spiral arteries, all are true except A First wave occurs before 12 weeks and consists of invasion upto border between decidua and myometrium. B Second wave occurs between 12 and 16 weeks with invasion of intramyometrial segments of spiral arteries. C Narrow lumen, muscular spiral arteries are converted into dilated, low resistance vessels. D Invasion by trophoblasts involves both decidual spiral arteries and decidual veins. 💡 Explanation Regarding, trophoblast invasion of maternal spiral arteries, all are true except ✓ Correct Answer: D. Invasion by trophoblasts involves both decidual spiral arteries and decidual veins.