The role of placental malperfusion in the pathogenesis of preeclampsia in dichorionic twin and singleton pregnancies

Introduction: In singletons, the pathogenesis of hypertensive disorders of pregnancy (HDP) is attributed to abnormal placentation, characterized by maternal vascular malperfusion (MVM) lesions. Whether MVM plays a similar role in twin pregnancies is unclear. The purpose of the study was to compared placental pathology findings between dichorionic-twin and singleton pregnancies complicated by HDP. Methods: Retrospective cohort study of women with dichorionic-twin or singleton pregnancies complicated by HDP who gave birth in a single tertiary center between 2001 and 2015. Placental abnormalities were classified into lesions associated with MVM, fetal vascular malperfusion, placental hemorrhage and chronic villitis. Placental findings and neonatal outcomes were compared between twin and singleton pregnancies. Results: A total of 144 women with twins and 768 women with a singleton pregnancy met the inclusion criteria. Compared with HDP singletons, twins with HDP had higher mean birth weights, were less likely to be small for gestational age and be born at < 34 and at < 32 weeks. Twins had lower odds for placental weight below < 10th percentile (aOR 0.49, 95%-CI 0.33-0.71), for MVM pathology (aOR 0.28, 95%-CI 0.20-0.39) and for fetal vascular malperfusion pathology (aOR 0.65, 95%-CI 0.45-0.93). These finding remained significant in the subpopulation of early onset HDP (< 34 weeks) and small for gestational newborn. Discussion: Our findings support the hypothesis that MVM are less relevant to the pathogenesis of HDP in twin pregnancies and suggest that other placental or non-placental factors are responsible for the increased risk of HDP in twin pregnancies.