Maternal Serum Screening is also called multiple marker screening test, triple screen, quad screen or loosely called AFP. It is a blood test that is given to all pregnant women. Typically it measures 3 chemicals in the blood -- AFP (Alpha-fetoprotein, made by the liver of the baby), hCG- (human Chorionic Gonadotropin, the pregnancy hormone) and estriol. That is why it is popularly called the triple marker. There is also a more advanced test called the quad marker test that measures a fourth substance called Inhibin-A.
This screening test signals possible birth defects such as Down's syndrome or neural tube defects. If the test shows abnormal results, then it does not mean that the baby has birth defects. It just requires further detailed diagnostic tests like Amniocentesis. Do not worry too much if you have abnormal test results. Most abnormal test results can be false alarms.
Usually between 15 and 18 weeks. If you are above 35 or have high risk for birth defects, this test should be conducted early around the 15th week to allow time for further diagnostic tests like amniocentesis (if need be).
How much time does it take for the results?