Gestational age standardized nuchal thickness values for estimating mid-trimester Down's syndrome risk

Area of Science:

• Prenatal diagnostics
• Fetal medicine
• Genetics

Background:

• Fetal nuchal thickening is a potential marker for chromosomal abnormalities.
• Accurate standardization of nuchal thickness measurements is crucial for reliable screening.
• Maternal age is a known risk factor for Down's syndrome.

Purpose of the Study:

• To develop gestational age-standardized indices for fetal nuchal thickening.
• To create a method combining nuchal thickness data with maternal age for Down's syndrome risk calculation.

Main Methods:

• Prospective measurement of nuchal thickness in pregnancies undergoing genetic amniocentesis.
• Development of regression equations for expected median nuchal thickness and calculation of multiples of the median (MoM) and percentage increase in nuchal thickness (PIN).
• Comparison of Down's syndrome detection efficiency using MoM, PIN, and direct nuchal thickness measurements, and evaluation of combined screening with maternal age.

Main Results:

• Both PIN and MoM values for nuchal thickness were highly correlated and poorly correlated with gestational age.
• Screening efficiency for Down's syndrome was not significantly different between PIN, MoM, and direct mm measurements.
• Incorporating nuchal thickness data (PIN or MoM) with maternal age significantly improved Down's syndrome screening efficiency (AUC increased from 0.58 to 0.79 for PIN and 0.77 for MoM).

Conclusions:

• Standardized nuchal thickness indices enable the integration of ultrasound data with maternal age.
• This combined approach allows for the derivation of individualized Down's syndrome odds.
• The developed method offers improved prenatal screening for Down's syndrome.