Second Trimester
Maternal Serum Multiple-Marker Screening (Triple Screen) Who Offered to all women When Between 15 and 18 weeks How A blood test Why This test checks for genetic abnormalities by measuring the level of a protein produced by the fetus called alpha-fetoprotein (AFP) as well as that of two hormones, human chorionic gonadotropin (hCG) and estriol. A high reading of AFP may signify a neural-tube defect. A low level may indicate Down syndrome. A new fourth screen can test levels of the hormone inhibin to better determine Down syndrome risk. Another test that would detect Down syndrome risk earlier in pregnancy is in development. Note: False positives of this test are common. Only 2 or 3 women in 100 who have low levels will actually be carrying a baby who has Down syndrome.
Glucose Screening Who Most women, but especially those who are overweight, are over 30, or have a family history of diabetes When 24 to 28 weeks How A blood test, which is done one hour after the mother drinks a sugary liquid Why To measure the blood-sugar level, which indicates the risk of gestational diabetes
Ultrasound (optional) Who Women whose doctors want to check fetal and uterine structure and development When Anytime, but usually between 15 and 20 weeks How A device called a transducer is placed either on the abdomen or in the vagina. Sound waves from the transducer create pictures of the fetus on a monitor and pick up the sounds of the fetal heartbeat. Why To establish the due date, check for multiple fetuses, monitor fetal growth, and look for structural abnormalities. New 3-D ultrasound machines can offer doctors a clearer image to better detect birth defects.
Amniocentesis (optional) Who Women over 35, those who have -- or whose partners have -- a family history of genetic diseases, and those whose multiple-marker test results are abnormal When Usually between 14 and 18 weeks How Guided by ultrasound, a doctor inserts a needle into the abdomen to draw a sample of amniotic fluid. Why To detect neural-tube defects, Down syndrome, and other genetic disorders. Note: The test carries with it a 1 in 200 risk of causing a women to miscarry.
