A Tournemire1, M Groussolles1, V Ehlinger2, A Lusque2, M Morin1, J B Benevent3, C Arnaud4, C Vayssière5. 1. Maternal Fetal Medicine Department, Hôpital Paule-de-Viguier, CHU de Toulouse, Toulouse, France. 2. UMR 1027 INSERM, Université Paul Sabatier Toulouse III, Toulouse, France. 3. Cabinet d'échographie des Pharaons, Toulouse, France. 4. UMR 1027 INSERM, Université Paul Sabatier Toulouse III, Toulouse, France; Clinical Epidemiology Unit, University Hospital, Toulouse, France. 5. Maternal Fetal Medicine Department, Hôpital Paule-de-Viguier, CHU de Toulouse, Toulouse, France; UMR 1027 INSERM, Université Paul Sabatier Toulouse III, Toulouse, France. Electronic address: christophe.vayssiere@gmail.com.
Abstract
OBJECTIVE: To assess the value of the prenasal thickness to nasal bone length ratio (PT/NBL) for detecting trisomy 21 (T21) after the first trimester. METHOD: Two examiners blinded to fetal T21 status retrospectively measured prenasal thickness (PT) and nasal bone length (NBL) of T21 and control fetuses at 15-36 weeks' gestational age on two-dimensional images from all T21-screening ultrasounds from November 2010 to April 2013. ROC curve analysis and its diagnostic values determined the best cut-off value for the ratio. Interobserver reproducibility was assessed. RESULTS: Good quality ultrasound profile images were available for 26 fetuses with T21 compared to 91 normal fetuses. The median PT/NBL ratio was 1.28 for T21 and 0.73 for control fetuses (p<0.0001). The PT/NBL ratio performed significantly better (AUC 0.99; 95%CI 0.97-1) than either PT (0.82; 0.73-0.91) or NBL (0.91; 0.85-0.98). The optimal PT/NBL ratio cut-off was 0.98, with a sensitivity of 88.5% [76.2-100%] and a specificity of 100%. Interobserver variability was low. CONCLUSION: The PT/NBL ratio is a strong marker for detecting T21 in the second and third trimesters, significantly more effective than either indicator alone.
OBJECTIVE: To assess the value of the prenasal thickness to nasal bone length ratio (PT/NBL) for detecting trisomy 21 (T21) after the first trimester. METHOD: Two examiners blinded to fetal T21 status retrospectively measured prenasal thickness (PT) and nasal bone length (NBL) of T21 and control fetuses at 15-36 weeks' gestational age on two-dimensional images from all T21-screening ultrasounds from November 2010 to April 2013. ROC curve analysis and its diagnostic values determined the best cut-off value for the ratio. Interobserver reproducibility was assessed. RESULTS: Good quality ultrasound profile images were available for 26 fetuses with T21 compared to 91 normal fetuses. The median PT/NBL ratio was 1.28 for T21 and 0.73 for control fetuses (p<0.0001). The PT/NBL ratio performed significantly better (AUC 0.99; 95%CI 0.97-1) than either PT (0.82; 0.73-0.91) or NBL (0.91; 0.85-0.98). The optimal PT/NBL ratio cut-off was 0.98, with a sensitivity of 88.5% [76.2-100%] and a specificity of 100%. Interobserver variability was low. CONCLUSION: The PT/NBL ratio is a strong marker for detecting T21 in the second and third trimesters, significantly more effective than either indicator alone.