Answer:USMLE step 2 Mcq 74:A primigravida in the 17th week of her symptomless gestation is found,on ultrasound, to have evidence of placental tissue cvering the cervical os




Correct Answer: A

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.


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