RESUMEN
BACKGROUND: Preeclampsia in a first pregnancy is a strong risk factor for preeclampsia in a second pregnancy. Whether chronic hypertension developed after a first pregnancy (interpregnancy hypertension) affects the recurrence risk of preeclampsia is unknown. METHODS: This is a population-based cohort study of 391,645 women with their first and second singleton births between 2006 and 2017. Exposure groups were women with preeclampsia in their first pregnancy, interpregnancy hypertension, or both risk factors. Women with neither risk factor were used as a reference group. We calculated the adjusted relative risk (aRR) with 95% confidence intervals (CIs) for overall preeclampsia in the second pregnancy as well as preterm (<37 gestational weeks) and term (≥37 gestational weeks) subgroups of the disease. RESULTS: Women with preeclampsia in their first pregnancy who did or did not develop interpregnancy hypertension had rates of preeclampsia in their second pregnancy of 21.5% and 13.6%, respectively. In the same population, the corresponding rates of preterm preeclampsia were 5.5% and 2.6%, respectively. After adjusting for maternal factors, women with preeclampsia in their first pregnancy who developed interpregnancy hypertension and those who did not have almost the same risk of overall preeclampsia in their second pregnancy (aRRs with 95% CIs: 14.51; 11.77-17.89 and 12.83; 12.09-13.62, respectively). However, preeclampsia in the first pregnancy and interpregnancy hypertension had a synergistic interaction on the outcome of preterm preeclampsia (aRR with 95% CI 26.66; 17.44-40.80). CONCLUSIONS: Women with previous preeclampsia who developed interpregnancy hypertension had a very high rate of preterm preeclampsia in a second pregnancy, and the two risk factors had a synergistic interaction.