Dichorionic versus monochorionic twin pregnancies and the risk of pre-eclampsia: a systematic review and meta-analysis

Objective To evaluate whether chorionicity influences the risk of pre-eclampsia (PE) in twin pregnancies by comparing maternal hypertensive outcomes between monochorionic (MC) and dichorionic (DC) gestations. Data sources PubMed, Embase, and the Cochrane Central Register of Controlled Trials were searched from inception to May 2026. The outcomes of interest were PE, gestational hypertension (GH), hypertensive disorders of pregnancy (HDP), and gestational age at delivery. Methods Random-effects meta-analyses were performed to pool risk ratios and mean differences with 95% confidence intervals (CIs). Heterogeneity was assessed using the I 2 statistic. Certainty of evidence was evaluated using the GRADE framework. Results Sixteen observational studies comprising 17,619 twin pregnancies (MC = 4017; DC = 13,602) were included. No significant differences were observed for PE (RR 0.88; 95% CI 0.63 to 1.22; I 2 = 65%), HDP (RR 0.69; 95% CI 0.32 to 1.49; I 2 = 70%), or GH (RR 0.98; 95% CI 0.59 to 1.63; I 2 = 44%). MC twins delivered earlier than DC twins (MD -0.90 weeks; 95% CI -1.12 to −0.67; I 2 = 44%). Sensitivity analyses confirmed robustness, and no publication bias was detected. Certainty of evidence was very low across outcomes. Conclusions Chorionicity does not appear to be associated with risk of PE or other HDP in twin pregnancies. MC gestations are associated with earlier delivery; however, overall maternal hypertensive risk appears comparable. Given the very low certainty of evidence, further prospective studies with standardized definitions and adequate confounder adjustment are needed.