History of abortion,preterm, term birth,and risk of preeclampsia: a population-based study

OBJECTIVE: The objective of this study was to examine the effect of previous abortion and preterm and term birth on the incidence of preeclampsia in subsequent pregnancies. STUDY DESIGN: A population-based retrospective cohort study was conducted that was based on 140,773 pregnancies that had delivered between 1993 and 1999 in 49 hospitals in Northern and Central Alberta, Canada. Multivariate logistic regression was applied to estimate odds ratios, with 95% confidence intervals, and to control for confounding variables. RESULTS: No significant difference was found in the incidence of preeclampsia in nulliparous women with previous abortion (2.6%) as compared to nulliparous women without previous abortion (2.9%; adjusted odds ratio, 0.89; 95% confidence interval, 0.78-1.01; P >.05). A single previous abortion was associated with a slightly decreased risk of preeclampsia (adjusted odds ratio, 0.84; 95% confidence interval, 0.72-0.97; P <.05). However, 2 and > or =3 abortions were not associated with a decreased risk of preeclampsia. In women with no history of previous abortion and term pregnancy, there was no significant difference in incidence of preeclampsia between women who had previous preterm birth (2.7%) and primigravid women (2.8%; adjusted odds ratio, 0.71; 95% confidence ratio, 0.48-1.03; P >.05). However, > or =2 previous preterm births were associated with a decreased risk of preeclampsia (adjusted odds ratio, 0.28; 95% confidence interval, 0.09-0.84; P <.01). The incidence of preeclampsia was markedly lower in multiparous women who previously delivered at term (0.9%) as compared to the incidence in primigravida women (2.9%; adjusted odds ratio, 0.29; 95% confidence interval, 0.26-0.33; P <.001). The adjusted odds ratios of preeclampsia for women with 1, 2, 3, and > or =4 previous term pregnancies were 0.32 (95% confidence interval, 0.28-0.36), 0.27 (95% confidence interval, 0.22-0.34), 0.22 (95% confidence interval, 0.15-0.33), and 0.21 (95% confidence interval, 0.12-0.35), respectively. CONCLUSION: A history of term pregnancy (> or =37 weeks) conveys a substantial "protection" against preeclampsia in the subsequent pregnancy.