The rate of abnormal human placentation has risen dramatically, with an increased risk of placenta accreta in older women, women with placenta previa in the present pregnancy, and those with a previous cesarean delivery (CD). This case-control study was performed to determine the association between placenta accreta in a pregnancy complicated by placenta previa and the type of primary CD.
Parturients with placenta accreta and placenta previa from 1993 to 2008 were included. Data analysis examined the effects of delivery mode for the primary CD on the development of placenta accreta or its variants in a pregnancy complicated by placenta previa. The primary outcome was the influence of the indication for the primary CD (elective without labor or emergency after some labor) on the subsequent risk of developing placenta accreta. Secondary outcomes were the risk of placenta accreta considering parity, gravidity, uterine surgery before the primary CD, and vaginal delivery before and after the primary CD. Criteria for controls included placenta previa, delivery during the study period, and a history of 1 or more CDs. Statistical analysis was performed using SPSS version 18 for Windows and Logxact 8.1. All tests were 2 sided, and P < 0.05 indicated statistical significance.
From 82,667 live births, 88 cases of placenta accreta were identified. The final cohort included 65 women with placenta accreta or variants matched with 101 controls; 67% of cases and 38% of controls delivered at less than 37 weeks’ gestation. Thirty-seven cases (56.9%) had placenta accreta, 15 (23.1%) had placenta increta, and 13 (20.0%) had placenta percreta. Cases and controls differed neither in maternal age, gravidity, or parity nor in other demographic or socioeconomic factors (all P > 0.05). A primary elective CD was performed in 46.2% of the cases and 18.6% of controls (P < 0.001). For women with primary emergency CD, significant differences were noted between cases and controls neither in cervical dilatation or length of labor in the primary labor nor in gestational age or presentation when the primary CD occurred without labor. Compared with women in whom the primary CD occurred after some labor, women whose primary CD occurred without labor were significantly more likely to develop placenta accreta (adjusted odds ratio [aOR], 3.00; 95% confidence interval [CI], 1.47–6.12; P = 0.025). Gravidity (aOR, 0.79; 95% CI, 0.61–1.03, P = 0.063), parity (aOR, 1.12; 95% CI, 0.75–1.66; P = 0.588), previous vaginal delivery (aOR, 0.85; 95% CI, 0.60–1.21; P = 0.364), and previous uterine surgery (aOR, 1.06; 95% CI, 0.53–2.15; P = 0.866) were not associated with placenta accreta with coexisting placenta previa.
Women who undergo a primary CD without labor are 3 times more likely to develop placenta accreta in a subsequent pregnancy complicated by placenta previa than women whose primary CD occurred after labor onset. Clinicians should be aware of this risk when counseling women for whom CD is an option. They should consider limiting the availability of elective CD as a choice to women in whom the alternatives of labor with vaginal delivery or the possibility of an emergency CD pose an unacceptable risk to her and the fetus’s well-being.
School of Women’s and Infants’ Health, University of Western Australia, Crawley, WA, Australia