Risk factors and perinatal outcomes for persistent placenta previa in nulliparas.

BACKGROUND: Placenta previa diagnosed on midtrimester ultrasound often resolves by the third trimester. Multiparity and previous cesarean delivery have been associated with persistence of placenta previa at delivery. Risk factors for persistent placenta previa in nulliparas are not well characterized. OBJECTIVE: This study aimed to identify risk factors for persistent placenta previa in the nulliparous population, and evaluate differences in outcomes between persistent and resolved placenta previa. STUDY DESIGN: This was a secondary analysis of the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-be (nuMoM2b), a prospective cohort study that observed 10,037 nulliparous individuals throughout pregnancy. Nulliparas diagnosed with placenta previa on midtrimester ultrasound were included in this analysis. Baseline characteristics and delivery outcomes of nulliparas with persistent placenta previa were compared with those of nulliparas with resolved placenta previa. Multivariate logistic regression with stepwise model selection was used for adjusted analyses. RESULTS: A total of 171 nulliparas (1.7%) in the nuMoM2b study were diagnosed with placenta previa on midtrimester ultrasound, of whom 17% (n=29) had persistent placenta previa at delivery. When compared with those with resolved placenta previa, nulliparas with persistent placenta previa were more likely to be older (median, 32 years [interquartile range, 30-37] vs 29 years [interquartile range, 25-31]; P<.01), have a previous pregnancy of <20 weeks (48.3% vs 22.5%; P=.01), have a previous dilation and curettage/evacuation procedure (27.6% vs 10.6%; P=.03), or have a pregnancy that resulted from assisted reproductive technology (31% vs 4.9%; P=.01). After adjusting for potential confounders, maternal age (adjusted odds ratio, 1.11; 95% confidence interval, 1.02-1.21), in vitro fertilization (adjusted odds ratio, 9.00; 95% confidence interval, 1.97-41.14), and previous pregnancy of <20 weeks (adjusted odds ratio, 2.77; 95% confidence interval, 1.10-6.95) remained statistically significant risk factors for persistent placenta previa. Persistent placenta previa was also associated with higher likelihood of antepartum admission (10.3% vs 0%; P<.01), preterm delivery (34.5% vs 12%; P<.01), lower neonatal birthweight (median, 2847 g [interquartile range, 2655-3310] vs 3263 g [interquartile range, 2855-3560]), and cesarean delivery (100% vs 20.4%; P<.001), but there were no differences in overall pregnancy or neonatal outcomes. CONCLUSION: In nulliparous individuals diagnosed with placenta previa on midtrimester ultrasound, older maternal age, previous pregnancy of <20 weeks, and in vitro fertilization are associated with persistent placenta previa at delivery.