The quad screen test is a screening method typically employed when first-trimester screening (including blood tests and ultrasound examination) is not available, or when prenatal check-ups begin in the second trimester. This test measures the levels of the following four markers, providing information about certain genetic conditions and birth defects:
* Alpha-fetoprotein (AFP): A protein produced by the developing baby.
* Chorionic gonadotropin (HCG): A hormone produced by the placenta.
* Estriol: A hormone produced by the placenta and the baby's liver.
* Inhibin A: Another hormone produced by the placenta.