Incidence of pre-eclampsia in first full-term pregnancies preceded by abortion

The incidence of preeclampsia in 1st term pregnancies was studied in relation to whether or not they were preceded by pregnancies which ended in abortion--spontaneous or induced. 220 patients with previous abortion were studied along with 2 sets of controls, 1 with no previous abortion or pregnancy and 1 with a 2nd term pregnancy. The incidence of preeclampsia was significantly lower than there had been a previous induced abortion but this was not as low as in cases with a 2nd term pregnancy. This finding may be interpreted as supporting the idea that pregnancy exerts a protective effect against the risk of preeclampsia which may have an immunological basis. A mechanism is suggested to explain the apparent "protective" effect of 1st pregnancies.