What pattern is observed on a quad screen for trisomy 18?

In the case of trisomy 18 (Edwards syndrome), the quad screen test typically shows a specific pattern where all markers are low. The quad screen measures four specific markers in maternal serum: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), estriol (uE3), and inhibin A.

For trisomy 18, it is characteristic to find that levels of these markers are decreased across the board. This low level pattern is particularly important for screening purposes, as it distinguishes trisomy 18 from other conditions, such as trisomy 21, where certain markers may be elevated or shown in different combinations. The reduced levels are due to the underlying issues with fetal development associated with trisomy 18.

Recognizing this pattern can aid clinicians in identifying patients who may benefit from further diagnostic testing, such as amniocentesis or chorionic villus sampling. Understanding the implications of the findings on the quad screen can significantly influence the management and counseling provided to patients at risk.