Previous cesarean birth. A risk factor for placenta previa

OBJECTIVE: To study the risk of placenta previa follow-ing a previous cesarean birth. STUDY DESIGN: We conducted a population-based, case-control study using 1990 North Carolina state birth certificate data. The study population included 342 women with a pregnancy complicated by placenta previa and 1,082 randomly selected controls. Analysis was restricted to women who reported one or more previous live births and delivered a singleton, live neonate. Adjusted odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated using logistic regression, controlling for maternal age, race, prior spontaneous or induced abortions and cigarette use. RESULTS: When the data were adjusted for maternal age, race, prior spontaneous or induced abortions, and cigarette use, women who had a previous cesarean birth and had a parity of3 were 1.7 times more likely (OR 1.7, 95% CI 0. 7, 4.2 ) and women of parity ≥ 4 were 5.5 times more likely (OR 5.5, 95% CI 1.0, 30:1) to have placenta previa than women of parity 1 who had a previous cesarean birth. CONCLUSION: Women with a history ofa previous cesarean birth and parity ≥ 3 were at increased risk of having a pregnancy complicated by placenta previa.