The Role of Chorionicity in Placenta-Related Disorders

Twin pregnancy is associated with higher rates of maternal morbidities including gestational diabetes and hypertension. Dichorionic twins are believed to have greater placental mass. Our objective was to study the incidence of two placenta-related disorders: gestational diabetes and hypertension, in dichorionic versus monochorionic twin pregnancies.

Patients' data of all consecutive twin pregnancies over a period of 12 years were collected from medical records. Data on chorionicity were retrieved from 1st trimester ultrasound reports. Maternal complications including gestational hypertension and diabetes were collected, and incidence was compared between dichorionic and monochorionic twin pregnancies. Records lacking chorionicity data and cases with pregestational diabetes were excluded.

A total of 960 twin pregnancies, 121 monochorionic and 839 dichorionic, were included. Average maternal age did not differ significantly between the groups. The median gestational age at delivery was 36.0 weeks in monochorionic and 36.7 in dichorionic twins. Primiparity (40.4% vs. 23.1%, p < 0.001) and the rate of infertility treatments (51.5% vs. 7.4%, p < 0.001) were both more common in the dichorionic group. The incidence of gestational hypertension disorders was 14% in monochorionic versus 11% in dichorionic twins (p = 0.36). Gestational diabetes was more common in dichorionic compared to monochorionic twins (9.4% and 2.5%, respectively); however, logistic multivariate analysis showed that gestational diabetes was highly correlated with maternal age (p < 0.001) and infertility treatments (p < 0.001) but not with chorionicity (p = 0.136).

Our results may imply that greater placental mass does not increase the risk for gestational hypertension and diabetes. This might support the role of additional multiple maternal factors associated with these complications.