<b>Assessment of Umbilical Cord Doppler Indices at Placental Insertion, Abdominal Insertion and Free-Floating Region in 2nd Trimester</b>

Background: Umbilical artery Doppler ultrasonography is widely used to assess fetoplacental circulation, but measured Doppler indices may vary according to the anatomical sampling site along the umbilical cord. Objective: To compare umbilical artery pulsatility index, resistive index, and systolic/diastolic ratio measured at placental insertion, fetal abdominal insertion, and the free-floating region of the umbilical cord. Methods: This cross-sectional repeated-measures observational study included 68 pregnant women aged 18–38 years with gestational age ranging from 20 to 38 weeks. Doppler assessment was performed using a 3–5 MHz curvilinear transabdominal transducer with color and pulsed-wave Doppler. Pulsatility index, resistive index, and systolic/diastolic ratio were recorded at the placental insertion, fetal abdominal insertion, and free-floating cord region. Data were analyzed using descriptive statistics, Wilcoxon signed-rank tests for pairwise site comparisons, and Spearman correlation analysis. Results: The placental insertion site showed lower mean pulsatility index, resistive index, and systolic/diastolic ratio values than the abdominal insertion and free-floating regions. Pairwise comparisons showed significant differences between placental and abdominal sites and between placental and free-floating sites for all three indices (p < 0.001), while abdominal and free-floating measurements did not differ significantly. Matched Doppler indices showed strong positive correlations across sites. Conclusion: Umbilical artery Doppler values vary by cord sampling site, with lower resistance indices at placental insertion. Standardized documentation of sampling location is important for accurate Doppler interpretation.