To see if pregnancy outcomes related with hypertensive disorders of pregnancy differed significantly between twin and singleton pregnancies. Between 2012 and 2019, researchers conducted a retrospective, population-based cohort analysis of all women who had a liveborn singleton or twin hospital delivery in Ontario, Canada. The Better Outcomes Registry and Network Ontario provided the data. Pregnancy outcomes were examined in twin gestations and separately in singleton gestations between women with and without hypertensive disorders of pregnancy. Overall, 932,218 women met the research requirements, with 917,542 having singleton pregnancies and 14,676 having twin pregnancies. The prevalence of hypertensive disorders during pregnancy was greater in twin gestations than in singleton gestations. Hypertensive disorders of pregnancy were linked to some negative outcomes in singleton gestations alone, as well as other negative outcomes in both singleton and twin gestations, however the aRR was lower in twins. Preterm delivery before 37 weeks of gestation, for example, and newborn respiratory illness. These findings held true in preeclampsia and early-onset preeclampsia subgroups of women.

Although the absolute risk of poor maternal and newborn outcomes is higher in twin pregnancies than in singleton pregnancies, the incremental risk of ill outcomes related with hypertension diseases in twin pregnancies is lower. These findings may be due in part to twin pregnancies having a greater baseline risk of preterm delivery and poor maternal and perinatal outcomes than singleton pregnancies.