• Q Yang, S W Wen, L Oppenheimer, X K Chen, D Black, J Gao, and M C Walker.
• OMNI Research Group, Clinical Epidemiology Program, Ottawa Health Research Institute, Ontario, Canada. qyang@ohri.ca
• BJOG. 2007 May 1;114(5):609-13.

ObjectiveTo quantify the risk of placenta praevia and placental abruption in singleton, second pregnancies after a caesarean delivery of the first pregnancy.DesignRetrospective cohort study.SettingLinked birth and infant mortality database of the USA between 1995 and 2000.PopulationA total of 5,146,742 singleton second pregnancies were available for the final analysis after excluding missing information.MethodsMultiple logistic regressions were used to describe the relationship between caesarean section at first birth and placenta praevia and placental abruption in second-birth singletons.Main Outcome MeasuresPlacenta praevia and placental abruption.ResultsPlacenta praevia was recorded in 4.4 per 1000 second-birth singletons whose first births delivered by caesarean section and 2.7 per 1000 second-birth singletons whose first births delivered vaginally. About 6.8 per 1000 births were complicated with placental abruption in second-birth singletons whose first births delivered by caesarean section and 4.8 per 1000 birth in second-birth singletons whose first births delivered vaginally. The adjusted odds ratio (95% CIs) of previous caesarean section for placenta praevia in following second pregnancies was 1.47 (1.41, 1.52) after controlling for maternal age, race, education, marital status, maternal drinking and smoking during pregnancy, adequacy of prenatal care, and fetal gender. The corresponding figure for placental abruption was 1.40 (1.36, 1.45).ConclusionCaesarean section for first live birth is associated with a 47% increased risk of placenta praevia and 40% increased risk of placental abruption in second pregnancy with a singleton.

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