This is a routine screen (tests) used to check for fetal abnormalities such as Down syndrome and neural tube defects. Down Syndrome is a chromosomal abnormality, sometimes called Trisomy 21. Neural tube defects are serious birth defects. The brain, spinal cord, or their coverings do not develop completely. Women should be tested in the 15th to 20th week of pregnancy. The msAFP screen involves three or four tests that measure substances found in the blood that make the testing better. During development, AFP levels in fetal blood and amniotic fluid rise until about 12 weeks. The levels then gradually fall until birth. AFP is a protein produce by fetal tissue. AFP crosses the placenta and appears in the maternal blood. A baby with an open neural tube defect has an opening in its spine, head, or abdominal wall that allows higher-than-usual amounts of AFP to pass into the mother's blood.
If a screen is positive, more tests are needed to make a diagnosis. These include ultrasound and perhaps amniocentesis (checking the fluid that surrounds the baby). These tests are used to help women and their caregivers make decisions about the management of their pregnancies.
In pregnancies where the fetus is carrying the chromosomal defect that results in Down syndrome, the levels of AFP and unconjugated estriol tend to be low and hCG and inhibin A levels high.
PREPARATION FOR TEST
Blood is drawn from a vein in your arm usually between the 15th and 20th weeks of pregnancy. Four different tests on your blood are done. These are AFP, hCG, unconjugated estriol, and inhibin A. The combination of tests produces a more accurate result.
Adult: less than 40ng/mL or less than 40 mg/L (SI units)
Child younger than1 year: less than 30 ng/mL
Ranges are stratified by weeks of gestation and vary among laboratories.
Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.
MEANING OF TEST
These are screening tests. Not all fetal abnormalities will give positive test results. Of all women who have positive AFP screening results, only a very small number of them have babies who actually have a neural tube defect or chromosomal abnormality. Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.
OBTAINING THE TEST RESULTS
It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.