If this pregnancy is complicated by recurrent placenta previa, then she is at significantly increased risk for placenta accreta.
Educational Objective:
List risk factors in a patient’s obstetric history that may complicate pregnancy in regard to placental abnormalities.
Key Point:
A prior history of placental abruption and prior history of placenta previa are the most significant risk factors for an abruption or previa in a subsequent pregnancy. Placenta accreta is associated with significant maternal and fetal morbidity; its risk significantly increases in the setting of current placenta previa with a history of cesarean delivery.
Explanation:
Placenta accreta occurs when placental villi adhere to the myometrium, making the placenta unable to separate after delivery. Life-threatening hemorrhage occurs if an attempt is made to detach the placenta. Delivery is usually performed by planned preterm cesarean hysterectomy. In the absence of placenta previa, this patient’s risk of accreta is 0.2%. Her risk of accreta dramatically increases to 11% in the presence of placenta previa.
The most significant risk factor for placental abruption is abruption in a prior pregnancy. There is a 20-fold risk increase for recurrent abruption. This is independent of the extent of abruption, although the recurrence risk increases further with history of severe abruption. Severe abruption is defined as one associated with significant maternal, fetal, and/or neonatal morbidity or death. Maternal complications associated with severe placental abruption are disseminated intravascular coagulation, blood transfusion, hypovolemic shock, renal failure, hysterectomy, or death. Fetal complications include a nonreassuring fetal status, intrauterine growth restriction, and intrauterine fetal demise. Neonatal complications include preterm delivery, small for gestational age, and neonatal death. Acute disseminated intravascular coagulation and fetal death are common when placental separation is more than 50%. In this patient’s history, it is not indicated whether or not it was a severe abruption, but she has an increased recurrence risk regardless of the severity of the abruption.
The patient is at increased risk for recurrent placenta previa. It recurs in 4% to 8% of pregnancies. A history of prior cesarean delivery is itself a risk for placenta previa. Increased risk solely due to cesarean delivery is 47% to 60% above the baseline risk. Because placenta previa is a risk factor for velamentous cord insertion, this patient is indirectly at increased risk for velamentous cord insertion.
The patient’s history by itself does not contraindicate vaginal delivery. In the absence of any of the common obstetric indications, she can have a trial of labor after cesarean delivery with a low transverse uterine incision and 1 prior cesarean delivery. Ideally, this patient should try for vaginal delivery. If she has placenta previa with a fourth pregnancy and she has had 2 prior cesarean deliveries, then she has a 40% to 50% risk of placenta accreta.
References:
Ananth CV, Lavery JA, Vintzileos AM, et al. Severe placental abruption: clinical definition and associations with maternal complications. Am J Obstet Gynecol. 2016;214(2):272.e1-272.e9.
Creasy RK, et al. Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice. 7th ed., 2014.
Gabbe SG, et al. Obstetrics: Normal and Problem Pregnancies. 7th ed., 2016.
Lockwood CJ, Russo-Stieglitz K. Placenta previa: epidemiology, clinical features, diagnosis, morbidity and mortality. Published 2017. Accessed April 27, 2018.
Resnik R, Silver RM Clinical features and diagnosis of the morbidly adherent placenta (placenta accreta, increta, and percreta). Published 2018. Accessed April 27, 2018.
