Alpha-Fetoprotein Testing
Alpha-fetoprotein (AFP) is a substance produced by the liver of the fetus, and its exact function is unknown. A blood test can be done, though, that measures the levels of AFP in a mother's blood, which can indicate the probability that the fetus has one of several serious birth defects.
An AFP test is only a screening tool. It does not diagnose a specific condition, it only indicates the increased risk of several birth defects. More specific tests, such as amniocentesis or chorionic villus sampling, must follow to make an accurate diagnosis.
It is very important that the doctor performing the test knows precisely the age of the fetus, since the level of AFP considered normal changes as the baby grows.
An abnormal test result does not necessarily mean that the baby will have a birth defect. AFP tests have a very wide range of abnormal results in order to prevent missing a fetus that has a serious condition.