Previous cesarean birth. A risk factor for placenta previa?

To study the risk of placenta previa following a previous cesarean birth.

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.

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 of 3 were 1.7 times more likely (OR 1.7, 95% CI 0.7, 4.2) and women of parity > or = 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.

Women with a history of a previous cesarean birth and parity > or = 3 were at increased risk of having a pregnancy complicated by placenta previa.