False positive rate in first trimester screening based on ultrasound and cfDNA vs. first-trimester combined screening with additional ultrasound markers
20 September 2018 (online)
To determine whether screening for trisomy 21 based on first trimester combined screening (FTCS) with assessment of the nasal bone (NB), the tricuspid (TCF) and the ductus-venosus-blood flow (DVF) results in similar false-positive-rates compared to the ultrasound and cfDNA screening.
This is a sub-analysis of a prospective randomized controlled study, which was performed between 2015 and 2016. Pregnant women with a normal first-trimester ultrasound examination at 11 to 13 weeks' gestation were randomized into two groups: FTCS with assessment of the NB, TCF and DVF (eFTCS) and ultrasound + cfDNA screening. The false-positive-rate in screening for trisomy 21 was defined as primary outcome parameter.
The study population consisted of 688 pregnancies in each study arm. In the eFCTS group, median delta NT was 0.0 mm, free beta-hCG and PAPP-A 0.96 and 1.11 MoM and the NB, TCF and DVF PIV abnormal in 0.9%, 0.6% and 7.0% cases. In the ultrasound + cfDNA group, median delta NT was 0.0 mm. In 10 pregnancies, the cfDNA analysis was uninformative and the risk for trisomy 21 was based on eFCTS. There were no false-positive cases in the ultrasound + cfDNA group, the false-positive-rates were between 0.9% and 2.2% with eFTCS.
Screening for trisomy 21 based ultrasound + cfDNA has a lower false-positive-rate than eFTCS.