AFP+ screening measures levels of certain substances (alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG) and unconjugated estriol (UE3)) in a pregnant woman's blood. These substances come from the fetus and placenta and are found in the blood of all pregnant women. It is normal for the levels of these substances to vary among different women, but some women with particularly high or low values may be at risk for having a baby with certain birth defects.
The AFP+ test is called a “screening test” because it cannot tell for certain whether the fetus does or does not have a birth defect. It can identify women who have a greater than average risk for having a baby with certain birth defects. About 7 or 8 of every 100 women who have AFP+ testing will need some further testing, but most of the time those women will deliver a normal, healthy baby. If you have an abnormal AFP+ test you can chose to have other tests (such as an ultrasound or amniocentesis) which can tell with greater certainty if a birth defect is present.
AFP+ is done between 15 and 20 weeks of pregnancy. It is used to screen for:
If the AFP+ test is normal, it does not guarantee a normal baby. This is a screening test and will detect 95% of fetuses with open neural tube defects, 60% of fetuses with Down syndrome, and 60-80% of fetuses with Trisomy 18. There are also many other kinds of problems that the AFP+ test cannot detect. But remember, most babies are born healthy.
If the AFP+ test indicates an increased risk for a birth defect, your care provider will discuss what to do next. Sometimes a repeat test or an ultrasound to confirm how far along you are will be recommended. In some cases you may be offered an amniocentesis or a consultation with a genetic counselor. Remember, most women who have further testing get normal results and have healthy babies.