Mid-trimester sonographic placenta previa thickness and persistence at delivery

Increasing placental thickness is associated with adverse outcomes including earlier gestational age at delivery, lower birthweight, and lower umbilical artery pH. We aim to determine whether mid-trimester placenta previa thickness is associated with persistence of previa at time of delivery.

Single-center retrospective cohort study of singleton gestations with previa diagnosed at 18-24 weeks delivering between 2015 and 2019. The thickest portion of the placenta was measured in a longitudinal plane on transabdominal imaging to determine placental thickness. We defined three cohorts: 1) thick placenta (>1 standard deviation above the mean), 2) thin placenta (>1 standard deviation below the mean), and 3) average placenta (within 1 standard deviation above or below the mean). Primary outcome was previa persistence at time of delivery. Secondary outcomes included postpartum hemorrhage, cesarean delivery, placenta accreta spectrum, and maternal morbidity composite (use of Bakri balloon, B-lynch, or O'Leary, peripartum hysterectomy, blood transfusion, ICU admission, or death). In all analyses, average thickness was used as the base comparator.

Of 239 pregnancies with mid-trimester previa there were 34 thin, 166 average, and 39 thick placentas. Patients with thick placenta were older, more likely to have prior cesarean delivery, fibroid uterus, and delivery at an earlier gestational age. After adjusting for confounders, thick placenta was associated with persistent previa (aOR 6.85 [3.13-15.00]) and cesarean delivery (aOR 2.76 [1.26-6.08]).

At diagnosis of mid-trimester previa, thick placenta is associated with persistence at time of delivery and delivery by cesarean section. This suggests placental thickness may assist with risk stratification and coordination of care.