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Nasal bone in first-trimester screening for trisomy 21
Simona Cicero1, Kyriaki Avgidou, Georgios Rembouskos
1Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, United Kingdom.
American Journal of Obstetrics and Gynecology
|July 4, 2006
Summary
Adding fetal nasal bone assessment to first-trimester screening significantly improves accuracy for trisomy 21. This method achieves a 90% detection rate with a reduced false-positive rate of 2.5%.
Area of Science:
- Prenatal diagnostics
- Genetics
- Fetal medicine
Background:
- First-trimester screening for trisomy 21 typically uses fetal nuchal translucency (NT) thickness and maternal serum biochemistry.
- The nasal bone's presence or absence is a potential marker for trisomy 21.
Purpose of the Study:
- To evaluate the impact of including fetal nasal bone assessment in first-trimester combined screening for trisomy 21.
- To determine if nasal bone assessment improves the detection rate (DR) and reduces the false-positive rate (FPR).
Main Methods:
- A prospective screening study involving 20,165 fetuses.
- Fetal nasal bone presence/absence was assessed alongside NT thickness and maternal serum markers (free beta-hCG and PAPP-A).
- Two screening strategies were compared: integrated screening and a two-stage approach with nasal bone assessment in intermediate-risk cases.
Main Results:
- The nasal bone was absent in 0.6% of normal fetuses and 62.1% of fetuses with trisomy 21.
- Combined NT and serum screening achieved a 90% DR at a 5% FPR.
- Including nasal bone assessment halved the FPR to 2.5% while maintaining the 90% DR.
Conclusions:
- Incorporating fetal nasal bone assessment into first-trimester combined screening enhances trisomy 21 detection.
- This integrated approach significantly reduces false positives, improving the overall screening efficacy.