The AFP test or Maternal Serum Alpha Fetoprotein test is a blood test of three determinants. It also contains estriol and human chorionic gonadotropin. The purpose of this test is to determine the risk of the current pregnancy being affected by certain chromosomal problems such as Down's syndrome or variants of spina bifida. Most of the counseling regarding this test is focused on Down's syndrome because it is the most common of the few problems detectable with this test.
Down's syndrome is a condition known to most people. It represents a group of problems which occur when there is an extra 21st chromosome. Down's syndrome patients have characteristic body changes such as short stature and mongoloid features. All are affected by variable levels of mental retardation. The risk of having a baby with Down's syndrome increases with maternal age. The risk at age 20 is 1/1,667; age 25 is 1/1,250; age 30 is 1/952; age 35 is 1/385; age 40 is 1/106 and age 45 is 1/30.
The AFP, or triple screen test, is a screening test and is not diagnostic. It will not tell you if your baby has Down's syndrome or any other problem. The test will indicate whether you should be offered further testing. The formula used to derive the risk approximates the risk of a 35-year old. Thus, a 35 year old patient is screen positive by virtue of age alone and will be offered further testing. Patients considered high risk because of age or a positive triple screen test, will be offered counseling with a perinatologist, ultrasound, and amniocentesis. Amniocentesis is the gold standard for diagnosis.
The AFP or triple screen test is optional. If you do not desire any further prenatal diagnostic information, don't get the test. If you want all the prenatal diagnostic information you can get so that you may prepare yourself for a potential special needs child or would consider termination, then get the test.