The effect of fetal number on the development of hypertensive conditions of pregnancy

OBJECTIVE: To estimate the incidence and effect of pregnancy-related hypertensive conditions on multiple gestations. METHODS: Women with 1-4 fetuses enrolled in an outpatient perinatal services program at 28 or more weeks of gestation were identified. Those without a prior diagnosis of hypertension at enrollment and who delivered at more than 28 weeks of gestation were included in the analysis. The incidence of all pregnancy-related hypertensive conditions, diagnosis of severe hypertensive conditions (hemolysis, elevated liver enzymes and low platelets syndrome; disseminated intravascular coagulation; eclampsia; low platelets; renal failure; and abruption), and interventional delivery related to hypertension were estimated, and compared according to fetal number. RESULTS: Data were analyzed for 34,374 singleton, twin, triplet, and quadruplet gestations. The incidence of pregnancy-related hypertensive conditions increased with multifetal gestations as compared with singletons (12.7-19.6% for multifetal gestations compared with 6.5% for singletons, P <.001). The incidence of severe pregnancy-related hypertensive conditions was significantly increased in twin (1.6%) and triplet (3.1%) gestations as compared with singletons (0.5%, P <.001). Quadruplet pregnancies were not significantly higher than triplet gestations for these complications. The need for early delivery related to hypertension was greater with increasing fetal number through triplet gestations. By logistic regression, higher fetal number, nulliparity, and advanced maternal age were each independently associated with the development of pregnancy-related hypertensive conditions. CONCLUSION: Mild and severe pregnancy-related hypertensive disease increases progressively with advancing fetal number from singleton to triplets but is not further increased in quadruplet pregnancies. Multifetal pregnancies should be observed closely for onset of gestational hypertensive disease.