Is placenta previa a determinant of preeclampsia?

Low implantation of the placenta has been reported to be associated with a decreased risk for preeclampsia and this has been attributed to increased placental blood flow. However, placenta previa is known to be associated with separation and bleeding, intrauterine growth retardation, and elevated umbilical blood flow resistance by Doppler studies, suggesting decreased umbilical blood flow. To better evaluate the relationship of placenta previa and preeclampsia, 6576 consecutive patients who had ultrasound examination after 28 weeks gestation and delivery at our institution were studied. The placental location, parity, maternal weight, development of preeclampsia, and gestational age were evaluated by using frequency tables and stepwise discriminant analysis. Results showed that placenta previa is not a significant determinant of the development of preeclampsia, but parity, maternal weight, and gestational age contributed significantly to the development of preeclampsia. The finding of decreased incidence of preeclampsia with previa is explained not by increased placental blood flow but by associated maternal characteristics, and particularly by the strong association of previa with premature delivery.