UKMLA PLAB AMC USMLE Prometric MCQ

Correct Answer: A

Explanation:
Gestational age at the time of the ultrasound examination greatly influences the incidence of placenta previa. At 17 weeks' gestation, evidence of placental tissue covering the cervical os will be found in 5 to 15 percent of all patients. However, more than 90 percent of these will resolve by term.This phenomenon has been termed placental migration. It is unlikely that the placenta actually separates and reattaches throughout the second and third trimesters. The changes in architecture secondary to differential growth of the lower uterine segment during the second and third trimesters probably account for this observation.