Amniocentesis is incorrect. Although it can be used to diagnose Down syndrome, it is not typically used to quantify risk.

Ultrasound is incorrect. While an ultrasound may show markers associated with Down syndrome, it cannot provide a definite diagnosis or quantify risk. It is also not typically used until later in the pregnancy.

Maternal serum quadruple screening is incorrect. It provides a probability of a fetus having Down syndrome, but it does not precisely quantify the risk.

Genetic familial history analysis is incorrect. While it is important to note a family history of Down syndrome, it doesn't quantify the risk of Down syndrome in the fetus. Down syndrome is typically not inherited; it is primarily caused by random chromosomal nondisjunction.