Final answer:
For Trisomy 18, the quad screen typically shows decreased MSAFP, Bhcg, estriol, and normal or decreased inhibin A. Trisomy is caused by nondisjunction resulting in an extra chromosome, and Trisomy 18 has a lower survival rate compared to Trisomy 21.
Step-by-step explanation:
The quad screen is a prenatal test that measures levels of four substances in the pregnant individual's blood. In Trisomy 18, or Edwards syndrome, expect to find an abnormal set of biomarker levels. The correct profile for Trisomy 18 is decreased MSAFP, decreased Bhcg, decreased estriol, and normal or decreased inhibin A, which would be option d: Decreased MSAFP, decreased Bhcg, decreased estriol, decreased inhibin A.
Trisomy arises due to nondisjunction, where chromosomes fail to separate properly during meiosis, leading to a diploid genotype with an extra chromosome. While Trisomy 21 (Down syndrome) individuals may often survive into adulthood, those with Trisomy 18 tend to have a lower survival rate, likely due to the consequences of having an extra chromosome 18, which causes more severe developmental issues.
It is also worth noting that the incidence of Trisomy 21 increases with maternal age, which is a significant risk factor for chromosomal anomalies like Trisomy 18 and Trisomy 21.