• Liran Hiersch, Joel G Ray, Jon Barrett, Howard Berger, Michael Geary, Sarah D McDonald, Christina Diong, Sima Gandhi, Jun Guan, Beth Murray-Davis, Nir Melamed, and DOH-NET (Diabetes, Obesity and Hypertension in Pregnancy Research Network).
• Division of Maternal-Fetal Medicine (Hiersch, Barrett, Melamed), Department of Obstetrics and Gynecology, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ont.; Departments of Obstetrics and Gynaecology (Hiersch), Lis Maternity Hospital and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel; Departments of Medicine and Obstetrics and Gynaecology (Ray), St. Michael's Hospital, University of Toronto; ICES Central (Ray, Diong, Gandhi, Guan); Division of Maternal-Fetal Medicine (Berger, Geary), Department of Obstetrics and Gynecology, St. Michael's Hospital, University of Toronto, Toronto, Ont.; Division of Maternal-Fetal Medicine (McDonald, Murray-Davis), Departments of Obstetrics and Gynecology, Radiology, and Research Methods, Evidence & Impact, McMaster University, Hamilton, Ont. liranh@tlvmc.gov.il.
• CMAJ. 2021 Sep 20; 193 (37): E1448-E1458.

BackgroundPeople whose singleton pregnancy is affected by hypertensive disorders of pregnancy (HDP) are at risk of future cardiovascular disease. It is unclear, however, whether this association can be extrapolated to twin pregnancies. We aimed to compare the association between HDP and future cardiovascular disease after twin and singleton pregnancies.MethodsWe conducted a population-based retrospective cohort study that included nulliparous people in Ontario, Canada, 1992-2017. We compared the future risk of cardiovascular disease among pregnant people from the following 4 groups: those who delivered a singleton without HDP (referent) and with HDP, and those who delivered twins either with or without HDP.ResultsThe populations of the 4 groups were as follows: 1 431 651 pregnant people in the singleton birth without HDP group; 98 631 singleton birth with HDP; 21 046 twin birth without HDP; and 4283 twin birth with HDP. The median duration of follow-up was 13 (interquartile range 7-20) years. The incidence rate of cardiovascular disease was lowest among those with a singleton or twin birth without HDP (0.72 and 0.74 per 1000 person-years, respectively). Compared with people with a singleton birth without HDP, the risk of cardiovascular disease was highest among those with a singleton birth and HDP (1.47 per 1000 person-years; adjusted hazard ratio [HR] 1.81 [95% confidence interval (CI) 1.72-1.90]), followed by people with a twin pregnancy and HDP (1.07 per 1000 person-years; adjusted HR 1.36 [95% CI 1.04-1.77]). The risk of the primary outcome after a twin pregnancy with HDP was lower than that after a singleton pregnancy with HDP (adjusted HR 0.74 [95% CI 0.57-0.97]), when compared directly.InterpretationIn a twin pregnancy, HDP are weaker risk factors for postpartum cardiovascular disease than in a singleton pregnancy.© 2021 CMA Joule Inc. or its licensors.

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