Additional performance of nasal bone in first trimester screening.

Area of Science:

• Prenatal diagnostics
• Fetal medicine
• Genetics

Background:

• First-trimester screening is crucial for detecting fetal aneuploidies like trisomy 21.
• Nuchal translucency (NT), maternal serum markers (free beta-hCG, PAPP-A), and maternal age are established screening parameters.
• The fetal nasal bone (NB) has been proposed as an additional ultrasound marker.

Purpose of the Study:

• To compare the screening performance for trisomy 21 in the first trimester.
• To evaluate the utility of including fetal nasal bone presence/absence in risk algorithms.
• To compare two Fetal Medicine Foundation (FMF) risk-assessment algorithms.

Main Methods:

• A cohort of 3174 patients underwent first-trimester screening (11-14 weeks gestation).
• Fetal trisomy 21 risk was calculated using two FMF algorithms: one without NB and one including NB.
• Screening components included maternal age, NT, free beta-hCG, PAPP-A, and NB status.

Main Results:

• The addition of fetal nasal bone (NB) to the risk algorithm did not improve the detection rate for trisomy 21.
• For a fixed 5% false-positive rate, detection rates were 72.2% (without NB) vs. 66.7% (with NB) for NT and serum markers, and 88.9% (without NB) vs. 83.3% (with NB) for all markers combined.
• Nasal bone was absent in 27.8% of trisomy 21 cases and 0.1% of normal cases.

Conclusions:

• Including fetal nasal bone presence or absence does not enhance the performance of first-trimester screening for Down syndrome.
• Individual risk-oriented two-stage screening may offer an alternative for integrating additional ultrasound markers.