Induced abortion: a risk factor for placenta previa.

A threefold increase in the incidence of placenta previa, from one in 318 deliveries (0.3%) in 1972-1974 to one in 109 deliveries (0.9%) in the twelve-month period ending June 30, 1980, was noted at Vanderbilt University Hospital. Two large groups of patients not present in 1972-1974 were found to be responsible for this increased incidence of placenta previa: one-way maternal transports and women who had had induced first trimester abortions. The frequency of maternal transports having placenta previa was 3.3% (p less than 0.0001), and the frequency of placenta previa in women after an induced first trimester abortion was 3.8% (p less than 0.0001). When correction for maternal transports was made, the endogenous induced first trimester abortion population had a frequency of placenta previa of 2.1% (p less than 0.004), whereas the remainder of the endogenous population had an incidence of placenta previa similar to that found in the years 1972-1974. Induced first trimester abortion is seen as a significant factor predisposing to placenta previa.