Alphafetoprotein Screen (AFP)
Genetic Screenings (AFP, Prenatal Risk Profile/Triple Screen, and Ultrasounds) seek to discern which pregnancies carry an increased risk of fetal abnormalities; it does NOT tell you which babies have abnormalities. Because of this, there can be false positives in the screening process which can be quite emotionally alarming to the parents if they don't understand this; the final word on whether your baby possesses the abnormality he/she is at risk for, often won't come until his/her birthday--which leaves many parents on edge for much of the nine months. Most women who do receive a "positive" in one of these tests (indicating increased risk of a fetal abnormality), however, go on to deliver a perfectly healthy baby. If you decide to participate in the genetic screening for whatever reason, and the results come back "abnormal", your provider will more than likely recommend further testing.
Diagnostic Tests (Chorionic Villus Sampling and Amniocentesis) can give you more accurate results, though the risks for the baby are much higher with these invasive tests.
Genetic screening, as with any test/procedure done during pregnancy, is entirely optional. You may choose to decline for any reason. In deciding whether or not a particular genetic screening is right for you and your baby, you will want to consider:
the benefits of the test--detection of abnormalities such as Downs Syndrome, spina bifida, etc.
the risks of the test--ranging from stress--sometimes undue--on the parents to loss of the baby (miscarriages can and do happen with many of these tests because of the test invasiveness--even to those babies who were otherwise perfectly healthy and thriving before the test)
acceptable courses of action for your family--it is often said that if an abortion is not an option for you, than genetic screening will not make any difference--other than possible limited preparation for the handicapped child
family history of genetic disorders
The Alphafetoprotein screening (AFP) is usually offered between 15-20 weeks in the pregnancy. This test seeks to find those pregnancies that are at an increased chance for neural tube defects (anecephaly, spina bifida, etc.) and Down syndrome. This test is done by checking the mother's blood levels of AFP--which is a substance produced in early pregnancy by the embryo's yolk sac, and later in pregnancy by the baby's liver.
It was discovered that mothers of babies with neural tube defects had unusually high amounts of AFP in their blood, whereas mother's of Down Syndrome babies had lower than normal amounts measured. Normal levels of AFP will rise and double about every 5 weeks during the second trimester. It is because of this that the test's high false positive rate, of about 20-35%, can probably be attributed. If the estimated gestation is incorrect, this test could possibly indicate a false positive; in essence, the levels would be considered either too high or too low for the pregnancy date. If the mother was thought to be 18 weeks, but really was only 14-15, the levels might be considered "abnormal", and further testing will be recommended.
Most of the risk associated with the AFP test comes, not from the test itself, but from what occurs as a result of the test--especially if the results yield a positive. Aside from the emotional stress that the parents will likely endure, worrying about whether their baby is "ok" or not, many of the follow up tests (usually ultrasounds and/or amniocentesis) which could be suggested are more invasive. These tests are usually more accurate in their findings, but also pose more of a risk to the baby-- most of the time, unnecessarily.
It is because of the high false positive rate of this test, that some providers are now suggesting the triple screen or Prenatal Risk Profile--a mix of AFP and other blood tests done at 16 weeks.