Prefrontal space ratio: comparison between trisomy 21 and euploid fetuses in the second trimester

Area of Science:

• Medical imaging
• Prenatal diagnostics
• Genetics

Background:

• Trisomy 21 (Down syndrome) is a common chromosomal disorder.
• Accurate prenatal detection is crucial for appropriate management.
• Existing ultrasound markers have limitations in sensitivity and specificity.

Purpose of the Study:

• To evaluate a novel ultrasound measurement, the prefrontal space ratio (PFSR).
• To assess the efficacy of PFSR in differentiating second-trimester trisomy 21 fetuses from euploid fetuses.

Main Methods:

• Analysis of stored 3D fetal ultrasound volumes from 26 trisomy 21 and 90 euploid fetuses (15-25 weeks' gestation).
• Calculation of PFSR using specific facial landmarks (mandible, maxilla, skull, and skin).
• Statistical comparison of PFSR distributions between groups and correlation with gestational age.

Main Results:

• PFSR was significantly lower in trisomy 21 fetuses (mean 0.36) compared to euploid fetuses (mean 1.48; P < 0.001).
• The PFSR demonstrated a wide range in both groups but showed clear separation.
• No significant association was found between PFSR and gestational age in either group.

Conclusions:

• The PFSR is a highly sensitive and specific ultrasound marker for trisomy 21 detection.
• This novel measurement shows promise for improved prenatal diagnosis of Down syndrome in the second trimester.