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The AFP screen is the most commonly available prenatal screening test for birth defects. AFP, a natural substance produced by baby's liver, normally enters the mother's bloodstream during pregnancy. Maternal levels of AFP are elevated if the mother is carrying a baby with a neural tube defect, NTD, (the vertebrae that normally enclose the spinal cord fail to develop), because AFP leaks out of an open spinal column. These defects include spina bifida (in which the spinal cord is not enclosed in the spinal column, often cause paralysis from the waist down) and anencephaly (in which baby's brain is either severely underdeveloped or doesn't develop at all). AFP levels are lower than normal if the baby has Down syndrome or another chromosomal defect.
The AFP screen is performed on a small amount of blood taken from the mother's arm. This common test is safe and is done between the sixteenth and eighteenth week of pregnancy. You will know the score within one week.
While the AFP screen is safe, it can be traumatic and lead to unnecessary worries. A confirmed positive test will be followed by other tests, which carry greater risks and anxiety, and in most cases, you find out there was nothing to worry about in the first place (or nothing you want to do about it anyway).
To decide whether or not to have a prenatal screening test for birth defects, consider these questions:Would the results matter to you?Would you change the course of your pregnancy? Are the results of the test going to create or alleviate anxiety?Would having the test or not having the test worry you more or less? Would knowing about a birth defect before hand dampen the joy of your pregnancy?If so, would it be better for you to have the time to prepare to handle a special needs baby?
Keep in mind that this screening is not very accurate. Ninety-five to ninety- eight percent of "positive high" or "positive low" AFPs turn out to be false (i.e., the baby has neither a chromosomal abnormality nor a neural tube defect). If your AFP test is abnormally high or abnormally low, your healthcare provider may recommend that you have further tests, such as an ultrasound and/or amniocentesis.