OC046: The use of nuchal translucency screening in women of 36 years and older: uptake and effects on invasive testing rate

Abstract

Objective: To evaluate the effectiveness of combined fetal screening by nuchal translucency (NT) thickness and ductus venosus blood flow assessment for the detection of chromosomal abnormalities. Methods: NT measurements and ductus venosus (DV) blood flow were prospectively evaluated in 839 consecutive fetuses between 11 and 14 weeks of gestation. Reverse or absent flow during atrial contraction in DV was defined abnormal. In 221 fetuses CVS was performed to analyse fetal karyotype. Fetal outcome was assessed by a written questionnaire of the obstetricians and in the liveborn postnatal outcome was obtained by neonatal assessment. The effectiveness for the detection of fetal chromosomal abnormality was calculated for NT measurement, DV blood flow assessment and the combined approach using the DV assessment as a second line test in fetuses with increased NT. Results: Karyotype was abnormal in 53 fetuses, NT-thickness was above the 95. percentile in 114 fetuses and DV blood flow pattern were abnormal in 52 fetuses. In the study population screen positive rate, sensitivity, specificity, positive predictive value and negative predictive value of abnormal DV flow pattern for chromosomal abnormality were 6.2%, 45.3%, 96.4%, 46.1%, and 96.3%. In this population NT screening yielded 13.6%, 84.9%, 39.5%, 98.9%, respectively. The corresponding values for the combined approach were 3.8%, 39.6%, 98.6%, 65.6% and 97.0%, respectively. Conclusions: DV blood flow assessment can be performed to screen for chromosomal abnormalities in fetuses at 11–14 weeks gestation. Our results suggest that the combined screening by NT and DV blood flow measurement yielded substantially lower detection rates of chromosomal abnormalities.