What is the expected beta-hCG level in a quad screen for a baby with trisomy 18?

In the context of chromosomal abnormalities such as trisomy 18, the expected beta-hCG level in a quad screen will be low. Trisomy 18, also known as Edwards syndrome, is associated with specific alterations in maternal serum markers. When screening for certain aneuploidies, the quad screen measures four substances, including alpha-fetoprotein (AFP), estriol (uE3), inhibin A, and human chorionic gonadotropin (hCG).

In cases of trisomy 18, the typical finding is a decrease in levels of beta-hCG compared to normal pregnancies. This is in contrast to the findings seen in trisomy 21 (Down syndrome), which usually presents with elevated levels of beta-hCG. Therefore, the low level of beta-hCG in the quad screen serves as a significant indicator pointing towards trisomy 18, among other clinical evaluations.

This understanding of the markers' behavior in chromosomal abnormalities helps clinicians not only in screening but also in counseling patients regarding risks and considerations surrounding their pregnancy.