The test is performed between 14th and 22nd week of pregnancy to measure three markers in a mother's blood i.e., Alpha-fetoprotein (AFP), Human Chorionic Gonadotropin (hCG) and Estriol. The test screens for the risk of chromosomal abnormalities such as Down syndrome (Trisomy 21) and neural tube defects like spina bifida. It is essential for early intervention and management options.