Role of Fetal Second Trimester 2D Ultrasound Facial Parameters in Down Syndrome Detection

Abstract

Introduction Down syndrome (DS) is the most common genetic cause of intellectual disability in humans. Various screening techniques are available, including the detection of facial characteristics of DS fetuses by prenatal ultrasonographic markers. Very few studies have tested the predictive validity of the markers in the Indian population. Objective This article determines the role of second trimester ultrasound in predicting DS using facial markers, namely, nasal bone length (NBL), prenasal thickness (PNT), NBL/PNT ratio, and PNT/NBL ratio in the Indian population Materials and Methods This prospective observational study recruited singleton pregnant women at 14 to 28 weeks of gestation with no comorbidities. Women with maternal disorders, abnormal amniotic fluid, and fetal structural anomalies were excluded. Three images of the midsagittal plane were obtained during a routine anomaly or well-being scan. The single “best” image was used for analysis. Scatter plots with regression lines and percentile curves for each gestation were created. Developed nomograms and scattered plots were validated by recruiting DS fetuses (diagnosed by amniocentesis and fetal karyotype). Results This study included 450 normal fetuses for developing nomograms, which were verified by matching 45 DS fetuses. The diagnostic accuracy of NBL, PNT, NBL/PNT ratios and PNT/NBL ratios was found to be 94, 99, 95, and 94.8, respectively. Sensitivity and specificity were found to be 51.11, 42.42, 48.89, 65.4 and 99, 96, 99.56, and 96.7 for NBL, PNT, NBL/PNT ratio, and PNT/NBL ratio, respectively. False negative rate and false positive rate were 38.89, 57.58, 51.11, 34.6 and 1, 4, 0.44, 3.3 for NBL, PNT, NBL/PNT ratio, PNT/NBL ratio, respectively. Conclusion High diagnostic accuracy was found for PNT, followed by NBL/PNT ratio, PNT/NBL ratio, and NBL. However, considering sensitivity and specificity markers together, we found the NBL/PNT ratio as a good diagnostic marker in predicting DS. Furthermore, the NBL/PNT ratio performs slightly better than its inverse counterpart (PNT/NBL ratio) for detecting DS fetuses, primarily because it produced less false positive cases.