Hypertensive disorders during monozygotic and dizygotic twin gestations: A population-based study

Objective: To determine whether the incidence of hypertensive disorders is different in monozygotic compared to dizygotic twin pregnancies. Methods: A registry-based survey of twin pregnancies delivered during 2003 to 2012. We used the best clinical estimate of zygosity based on the concept that all monochorionic twins are monozygotic and all unlike-sex pairs are dizygotic, thus excluding same-sex dichorionic twin gestations for which zygosity cannot be ascertained on clinical grounds. Study cohorts were twin pregnancies with or without preeclampsia and gestational hypertension. Results: A total of 3419 twin gestations met the inclusion criteria, of which 442 (12.9%) were monochorionic and 1255 (36.7%) were unlike-sex twins, excluding 1722 same-sex dichorionic twin gestations (50.4%). There was no significant difference in the incidence of preeclampsia (OR: 0.9; 95% CI: 0.4-2.0 for monozygotic males and OR: 0.6; 95% CI: 0.3-1.4 for monozygotic females) and gestational hypertension (OR: 0.7; 95% CI: 0.2-2.5 for monozygotic males, and OR: 0.7; 95% CI: 0.2-2.3 for monozygotic females) between monochorionic and unlike-sex pairs. Maternal prepregnancy obesity and nulliparity were the only significant associated factors of preeclampsia (OR: 3.8; 95% CI: 2.0-7.0, and OR: 2.5; 95% CI: 1.4-4.4, respectively). Maternal prepregnancy obesity (OR: 5.5; 95% CI: 2.5-12.2), maternal age 36 years (OR: 2.5; 95% CI: 1.1-6.1), and family history of hypertension (OR: 2.6; 95% CI: 1.3-5.1) were significantly associated with gestational hypertension. Conclusion: Based on a large population-based dataset and on the best clinical estimate of twin zygosity, it appears that zygosity is not associated with hypertensive disorders in twin gestations.