Diagnostic Performance of Prenatal Ultrasound to Detect Velamentous Cord Insertion in Twin Pregnancies

Objective: We aimed to determine the ability of prenatal ultrasound to detect velamentous cord insertion (VCI) in twin pregnancies and identify factors influencing diagnostic sensitivity. Methods: This single-center retrospective study included twins delivered between April 2018 and March 2024. We excluded monochorionic monoamniotic twins, those without chorionicity or umbilical cord insertion data, and fetuses that died in utero. Umbilical cord insertion sites assessed by second-trimester transabdominal ultrasound (16 + 0 to 21 + 6 weeks of gestation) using color Doppler imaging were classified as normal, marginal, or velamentous. The results of postnatal macroscopic examinations served as reference standards. We calculated accuracy, sensitivity, specificity, positive (PPV) and negative (NPV) predictive values. The effects of examiner expertise, chorionicity, placental location, ultrasound device, and maternal body mass index (BMI) on diagnostic sensitivity were analyzed in subgroups. Results: We confirmed VCI in 45 (8.8%) of 514 delivered fetuses. Prenatal ultrasound correctly identified 14 VCI cases. Sensitivity, specificity, PPV, and NPV were 31.1% (14/45), 98.9% (464/469), 73.7% (14/19), and 93.7% (464/495), respectively. The overall accuracy was 93.0% (478/514). Sensitivity was significantly higher when ultrasound specialists conducted examinations compared with non-specialists and when twins were monochorionic diamniotic twins than dichorionic. Anterior placental location and high-performance ultrasound equipment were also associated with increased sensitivity, but were not statistically significant. Maternal BMI did not affect diagnostic sensitivity. Conclusions: Prenatal ultrasonographic detection of VCI in twin pregnancies has high specificity but limited sensitivity. Diagnostic performance was influenced by examiners' experience and chorionicity. Routine assessment of cord insertion sites and targeted training might improve detection and support the optimized perinatal management of twin pregnancies.