Abstract
The incidence of pre-eclampsia in first term pregnancies was studied in relation to whether or not they were preceded by pregnancies which ended in abortion—spontaneous or induced. Two hundred and twenty patients with previous abortion were studied along with two sets of controls, one with no previous abortion or pregnancy and one with a second term pregnancy. The incidence of pre-eclampsia was significantly lower when there had been a previous induced abortion but this was not as low as in cases with a second term pregnancy. This finding may be interpreted as supporting the idea that pregnancy exerts a protective effect against the risk of pre-eclampsia which may have an immunological basis. A mechanism is suggested to explain the apparent ‘protective’ effect of first pregnancies.

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