Incidence, risk factors and perinatal outcomes for placenta accreta in Australia and New Zealand: A case-control study

Objective Estimate the incidence of placenta accreta and describe risk factors, clinical practice and perinatal outcomes. Design Case-control study. Setting Sites in Australia and New Zealand with at least 50 births per year. Participants Cases were women giving birth (≥20 weeks or fetus ≥400 g) who were diagnosed with placenta accreta by antenatal imaging, at operation or by pathology specimens between 2010 and 2012. Controls were two births immediately prior to a case. A total of 295 cases were included and 570 controls. Methods Data were collected using the Australasian Maternity Outcomes Surveillance System. Primary and secondary outcome measures Incidence, risk factors (eg, prior caesarean section (CS), maternal age) and clinical outcomes of placenta accreta (eg CS, hysterectomy and death). Results The incidence of placenta accreta was 44.2/100 000 women giving birth (95% CI 39.4 to 49.5); however, this may overestimated due to the case definition used. In primiparous women, an increased odds of placenta accreta was observed in older women (adjusted OR (AOR) women≥40 vs <30: 19.1, 95% CI 4.6 to 80.3) and current multiple birth (AOR: 6.1, 95% CI 1.1 to 34.1). In multiparous women, independent risk factors were prior CS (AOR ≥2 prior sections vs 0: 13.8, 95% CI 7.4 to 26.1) and current placenta praevia (AOR: 36.3, 95% CI 14.0 to 93.7). There were two maternal deaths (case fatality rate 0.7%). Women with placenta accreta were more likely to have a caesarean section (AOR: 4.6, 95% CI 2.7 to 7.6) to be admitted to the intensive care unit (ICU)/high dependency unit (AOR: 46.1, 95% CI 22.3 to 95.4) and to have a hysterectomy (AOR: 209.0, 95% CI 19.9 to 875.0). Babies born to women with placenta accreta were more likely to be preterm, be admitted to neonatal ICU and require resuscitation.