Risk of pre-eclampsia in first and subsequent pregnancies: prospective cohort study

Abstract

Objective: To investigate whether pre-eclampsia is more common in first pregnancies solely because fewer affected women, who presumably have a higher risk of recurrence, go on to have subsequent pregnancies.

Design: Prospective cohort study.

Setting: Swedish Medical Birth Register.

Participants: 763 795 primiparous mothers who had their first births in Sweden, 1987-2004.

Main outcome measures: Pre-eclampsia.

Results: The risk of pre-eclampsia was 4.1% in the first pregnancy and 1.7% in later pregnancies overall. However, the risk was 14.7% in the second pregnancy for women who had had pre-eclampsia in their first pregnancy and 31.9% for women who had had pre-eclampsia in the previous two pregnancies. The risk for multiparous women without a history of pre-eclampsia was around 1%. The incidence of pre-eclampsia associated with delivery before 34 weeks' gestation was 0.42% in primiparous women, 0.11% in multiparous women without a history of pre-eclampsia, and 6.8% and 12.5% in women who had had one or two previous pregnancies affected, respectively. The proportion of women who went on to have a further pregnancy was 4-5% lower after having a pregnancy with any pre-eclampsia but over 10% lower if pre-eclampsia was associated with very preterm delivery. The estimated risk of pre-eclampsia in parous women did not change with standardisation for pregnancy rates.

Conclusions: Having pre-eclampsia in one pregnancy is a poor predictor of subsequent pregnancy but a strong predictor for recurrence of pre-eclampsia in future gestations. The lower overall risk of pre-eclampsia among parous women was not explained by fewer conceptions among women who had had pre-eclampsia in a previous gestation. Early onset pre-eclampsia might be associated with a reduced likelihood of a future pregnancy and with more recurrences than late onset pre-eclampsia when there are further pregnancies. Findings are consistent with the existence of two distinct conditions: a severe recurrent early onset type affected by chronic factors, genetic or environmental, and a milder sporadic form affected by transient factors.

Fig 1 Risk of pre-eclampsia in given pregnancy by pregnancy order and history of pre-eclampsia, Swedish Medical Birth Register, 1987-2004

Fig 2 Risk of pre-eclampsia in second pregnancy by years since first pregnancy and history of pre-eclampsia, Swedish Medical Birth Register, 1987-2004

Fig 3 Risk of severe pre-eclampsia (defined as pre-eclampsia associated with delivery before 34 weeks) in given pregnancy by pregnancy order and history of pre-eclampsia, Swedish Medical Birth Register, 1987-2004