The impact of twin gestation on long-term maternal morbidity among women with hypertensive disorders of pregnancy

BACKGROUND: Hypertensive disorders of pregnancy (HDP) are associated with increased maternal morbidity. While long-term maternal outcomes following HDP have been studied in singleton gestations, data regarding twin pregnancies remain limited. OBJECTIVE: To assess whether the risk for long-term maternal metabolic, cardiovascular, and vascular morbidity differs between women diagnosed with HDP during twin vs singleton gestations; to evaluate the association between HDP severity and future morbidity, and the risk for HDP recurrence. STUDY DESIGN: A retrospective cohort study included women who delivered at a tertiary medical center between 1991 and 2021 and were insured by Clalit Health Services, with at least one diagnosis of HDP. The first HDP-affected pregnancy was defined as the index pregnancy. Women diagnosed with HDP during twin gestations were compared to those diagnosed during singleton gestations. Women with preexisting cardiometabolic disease prior to the index pregnancy were excluded. Long-term maternal outcomes included metabolic, cardiovascular, and vascular morbidity occurring after the index pregnancy, during a follow-up of up to 30 years. Cox proportional hazards models were used to estimate adjusted hazard ratios, adjusting for maternal age, ethnicity, gestational diabetes, and fertility treatments. RESULTS: The study included 10,853 women with HDP, of whom 487 (4.5%) had twin gestations and 10,366 (95.5%) had singleton gestations. Women with twin gestation were more likely to have severe preeclampsia and less likely to have mild preeclampsia compared with women with singleton gestations. Twin HDP were associated with lower risk of metabolic morbidity (56.9% compared with 64.0%, P=.001) and composite long-term morbidity (58.3% compared with 65.1%, P=.002). However, following adjustment in multivariable models, twin gestation was not independently associated with lower risk for any of the studied morbidities. A dose-response association was observed between HDP severity and long-term metabolic, vascular, and overall morbidity among singleton gestation, but not among twin gestation. Recurrence of preeclampsia in a subsequent singleton gestation was significantly lower following a twin-index pregnancy (17.8% compared with 30.6%, adjusted odds ratio 0.51, 95% confidence interval 0.36-0.73). CONCLUSION: Although women with HDP in twin gestations were more likely to have severe preeclampsia, twin gestation was not independently associated with long-term maternal metabolic, cardiovascular, vascular, or composite morbidity after adjustment for measured confounders. The lower observed recurrence of HDP after a twin-index pregnancy is an interesting and clinically relevant finding that warrants further investigation; however, selection factors or reproductive patterns should be considered when interpreting this association.