Diagnostic performance and feasibility of classifying placental umbilical cord insertion during routine prenatal ultrasound.

INTRODUCTION: Abnormal cord insertion (velamentous or marginal) is associated with adverse perinatal outcomes, and guidelines recommend prenatal diagnosis when feasible. However, the diagnostic performance and feasibility of classification of the placental cord insertion in an ultrasound screening setting remain uncertain. The aim of the study was to evaluate the feasibility and diagnostic performance of prenatal classification of placental cord insertion site. MATERIAL AND METHODS: This prospective observational study was conducted at a Norwegian tertiary center from May 2017 to August 2023. Pregnant women with singleton pregnancies attending the routine ultrasound scans were invited to participate and enrolled after written informed consent. During the scan, the distance between the umbilical cord insertion and the placental edge (the "test variable") was measured. At birth, cord insertion was categorized as normal, abnormal (velamentous (≤0 mm) or marginal (1-24 mm) from the placental edge), or unclassifiable. Diagnostic performance of the measured distance by ultrasound to predict insertion type at birth was evaluated using area under the receiver operating characteristic curve (AUC), with adjustment for covariates in Bayesian logistic regression, including sonographer experience. Sensitivity, specificity, and positive and negative predictive values, including optimal thresholds (Youden and Closest top-left criteria), were estimated. RESULTS: In total, 2859 examinations were carried out, and 2553 examinations in 1919 pregnancies were between 11 and 18 gestational weeks and included in the analyses. Of these, 634 had two examinations. Cord insertion site was classifiable in all but 14/2859 examinations (0.49%). The AUC for prenatal identification of abnormal cord insertion was 0.76. Using the Youden threshold, sensitivity was 0.64 and specificity 0.76; using the Closest top-left threshold, sensitivity was 0.69 and specificity 0.70. Negative predictive values exceeded 0.90, whereas positive predictive values (PPVs) were lower. Diagnostic performance was higher for velamentous cord insertion specifically (AUC = 0.89) than for abnormal insertion overall. Adjusting for additional covariates (operator experience and maternal characteristics) minimally affected AUC estimates. CONCLUSIONS: Assessment of the umbilical cord insertion during routine prenatal ultrasound was feasible and demonstrated high negative but limited PPV, suggesting that cord insertion assessment may be incorporated into routine antenatal imaging to support risk stratification.