Purpose of review
Placental implantation abnormalities (PIAs) comprise a large group of disorders associated with significant maternal, fetal, and neonatal morbidity.
Risk factors include prior uterine surgery/myometrial scarring and the presence of placenta previa with or without prior cesarean delivery. Newly identified risk factors include previous prelabor cesarean delivery and previous postpartum hemorrhage. PIAs contribute substantially to preterm birth with prematurity rates ranging from 38 to 82%. Diagnosis is typically made by ultrasound in the second or third trimester; transvaginal ultrasound and color Doppler are useful in evaluating for placental invasion, placental edge thickness, presence of fetal vessels, and cervical length. Suggestive MRI features include increased vascularity, dark T2 bands, uterine bulging, thin or indistinct myometrium, and loss of dark T2 interface. An important first-trimester finding is the implantation of the gestational sac into prior hysterotomy scar (cesarean scar pregnancy). Recommendations for delivery are universally preterm and based on expert opinion. Proposed management strategies are outlined depending on cervical length, distance between internal cervical os and placenta, and placental edge thickness.
There has been a recent shift in focus to individualizing management in order to improve delivery timing and in some cases even decrease risks associated with prematurity. There is a need for larger prospective studies or randomized trials to show that individualizing care can improve outcomes.