The likelihood of placenta previa with greater number of cesarean deliveries and higher parity

OBJECTIVE: To examine the relationship between prior cesarean delivery and placenta previa. METHODS: A hospital-based, case-control study was conducted in which 316 multiparous women with placenta previa were identified. Controls consisted of 2051 multiparous women with spontaneous vaginal deliveries. Information on prior cesarean delivery was examined in three forms: as a dichotomous variable, as an ordinal variable, and as a set of three indicator variables for one, two, and three or more cesarean deliveries. Multivariable logistic regression modeling was used to obtain an adjusted estimate of this association. RESULTS: Women with a prior cesarean delivery were more likely to have a placenta previa than those without (odds ratio OR] 1.59, 95% confidence interval CI] 1.21, 2.08). The likelihood of placenta previa increased as both parity and number of cesarean deliveries increased. Thus, the adjusted OR for a primiparous woman with one cesarean delivery was 1.28 (95% CI 0.82, 1.99). For a woman who has four or more deliveries with only a single cesarean delivery, the OR increases to 1.72 (95% CI 1.12, 2.64). This trend continues with greater parity and a greater number of cesarean deliveries such that the likelihood of placenta previa for a woman with parity greater than four and greater than four cesarean deliveries was OR 8.76 (95% CI 1.58, 48.53). CONCLUSION: This study supports the association between prior cesarean delivery and placenta previa and demonstrates that the joint effect of parity and prior cesarean delivery is greater than that of either variable alone.