Review: previous caesarean delivery or abortion increases the risk of placenta praevia
Question Does a history of caesarean deliveries, spontaneous abortions, or induced abortions increase the risk of placenta praevia?
Studies were identified by searching Medline databases using the keywords placenta praevia, placental disorders, antepartum haemorrhage, antepartum bleeding, caesarean delivery, caesarean section, uterine surgery, spontaneous abortion, induced abortion, and elective abortion; and by scanning bibliographies of relevant papers.
Studies were selected if they provided quantitative analysis of placenta praevia and were published in English between 1950 and 1996. Studies on placental abruption and case reports were excluded.
Data were extracted on the total number of pregnancies; the number of pregnancies complicated by placenta praevia; previous caesarean deliveries, spontaneous abortions, and induced abortions; study design; and the country in which the study was run. Odds ratios (ORs) were calculated using fixed and random effects models with results from random effects models considered to be more reliable due to evidence of heterogeneity among studies.
In 36 studies, 13 992 of 3 700 000 women who were pregnant had placenta praevia. The reported incidence was approximately …