A: An amniocentesis is an invasive procedure used to determine chromosomal abnormalities in women who have a high risk for of having a baby with a chromosomal abnormality. A small needle is placed into the uterus through the mother's belly and fluid containing fetal cells is removed; these cells are then tested for abnormalities. The earlier the amnio is done (between 14-17 weeks), the higher the risk of rupturing membranes and experiencing pregnancy loss. If the amnio is done between 18-22 weeks, there is a 1/200 or 1/250 risk of fetal loss, depending on the OB's experience.
The "Triple test" and "Quad screen" are simple blood tests that can be done between 15-20 weeks gestation and have no risk to the fetus or the mom.