Efficacy of the genetic sonogram in a stepwise sequential protocol for down syndrome screening

Area of Science:

• Medical screening
• Prenatal diagnostics
• Genetics

Background:

• Stepwise sequential screening is a common method for Down syndrome detection.
• Genetic sonograms offer additional ultrasound markers for fetal aneuploidy.

Purpose of the Study:

• To evaluate the efficacy of incorporating a genetic sonogram after stepwise sequential screening for Down syndrome.
• To assess the impact on detection rates and false-positive rates.

Main Methods:

• Retrospective cohort study of 6286 women undergoing stepwise sequential screening followed by a genetic sonogram.
• Down syndrome risk was recalculated using sonographic findings and likelihood ratios.
• Screen positivity was defined as a final risk of 1:270 or higher.

Main Results:

• Down syndrome detection rate slightly decreased from 88.2% to 82.4% after the genetic sonogram (non-significant).
• The false-positive rate decreased from 6.2% to 4.2% with the addition of the genetic sonogram.
• The genetic sonogram converted some screen-negative results to positive and some screen-positive results to negative.

Conclusions:

• Caution is advised when using genetic sonograms after prior screening.
• Negative sonogram results in screen-positive women may be falsely reassuring.
• For screen-negative women near the cutoff, sonography can aid decisions regarding amniocentesis.