Prenatal imaging phenotypes and outcomes of umbilical-portal-systemic venous shunts in singleton and twin pregnancies: A historical cohort study.

INTRODUCTION: To compare prenatal imaging phenotypes, primary structural anomalies, fetal growth restriction, and perinatal outcomes of umbilical-portal-systemic venous shunts between singleton and twin pregnancies. MATERIAL AND METHODS: This single-center historical cohort included fetuses with a prenatal diagnosis of an umbilical-portal-systemic venous shunt at Shanghai First Maternity and Infant Hospital from November 2019 to August 2023. The primary outcome was shunt subtype distribution by pregnancy type. Secondary outcomes were fetal growth restriction, primary structural anomalies, genetic findings, twin-specific complications, and perinatal outcomes. Shunts were classified as Type I, II, or III according to their vessel of origin. A post hoc analysis repeated the overall growth-restriction comparison after excluding fetuses with primary structural anomalies or abnormal genetic results. RESULTS: Sixty-three pregnancies, each contributing one fetus with UPSVS, were included: 37 singleton and 26 twin pregnancies. Twins were diagnosed earlier than singletons (22.7 ± 4.2 vs. 27.1 ± 5.4 weeks; p < 0.001). Subtype distribution differed between the groups: Type III predominated in singletons and Type II in twins (p < 0.001). Primary structural anomalies were found in 6/26 twins (23.1%) and 11/37 singletons (29.7%; p = 0.774). Genetic testing was performed in 44 fetuses, with abnormal results in 5/44 (11.4%). Fetal growth restriction was more frequent in twins (20/26, 76.9% vs. 17/37, 45.9%; p = 0.019). Among monochorionic pregnancies, 14/15 Type II cases had selective fetal growth restriction. The overall difference remained after fetuses with primary structural anomalies or abnormal genetic results were excluded (85.0% vs. 50.0%; p = 0.027). CONCLUSIONS: Shunt subtype distribution differed between singleton and twin pregnancies, and fetal growth restriction was more frequent in twins; primary structural anomaly rates were similar. Pregnancy type and chorionicity should be considered when interpreting prenatal findings. Larger studies with standardized postnatal imaging are needed to clarify prognosis and spontaneous closure.