343: Second trimester placenta previa and resolution patterns: a four year institutional review

To identify maternal and ultrasound characteristics that predict resolution of placenta previa diagnosed in the second trimester, both to improve patient counseling and to decrease the need for repeat ultrasounds evaluation. A retrospective review of singleton gestations diagnosed with placenta previa at >14 weeks' gestation from 12/2003 through 12/2007. Placenta previa was categorized as complete, marginal, or low lying. Maternal characteristics and ultrasound variables (anterior vs posterior, distance from the cervical os at initial ultrasound exam) were evaluated to see which would predict the timing of resolution of placenta previa. 670/ 23, 971 (2.8% of) patients had a placenta previa diagnosed in the 2nd trimester, of which 366 met study criteria. The mean gestational age at diagnosis was 18.5 wks (±3.4). 17% had a prior cesarean delivery. Complete previas were found more commonly than marginal/low-lying previas (67% versus 33%), and posterior location was more common than anterior location (65% versus 35%). The frequency of resolution for complete and marginal/low-lying previas was 84% and 98%, respectively. Only distance from the internal cervical os at the time of diagnosis predicted resolution of placenta previa. Neither maternal race, age, gravidity, parity, history of cesarean delivery, or placental location was significant. The mean gestational age of documented resolution was 28.6 weeks. By 34.2 weeks, 90% of all previas had resolved. Placenta previa is a common incidental finding at the time of routine second trimester ultrasound. Previously identified independent risk factors for placenta previa (advanced maternal age, prior cesarean delivery, and grand multiparity) do not appear to predict persistence of previa. Marginal and low lying previas diagnosed in the second trimester do not appear to warrant repeat ultrasound evaluation, although prospective studies would be needed to confirm this finding.