AFP Test
AFP Test or Alpha-fetoprotein test is conducted on pregnant women to check the AFP level in the blood. The liver in the fetus produces AFP naturally. Determining the amount of AFP in the mother's blood will help identify any neural tube defect in the fetus. Neural tube defects arise in 2 out of every 1,000 pregnancies. AFP test also helps check for Down's syndrome. There are 60% chances for detecting Down's syndrome when the AFP levels are low in the blood. AFP can also be calculated from the sample of amniotic fluid of a pregnant woman. This screening test is generally performed between 16 and 18 weeks of pregnancy and is very sensitive between 15 and 17 weeks. The accuracy of the AFP test result lies in the exact age of the fetus. The AFT test is also referred to as maternal serum alpha-fetoprotein (MSAFP). AFP test is done on men and non-pregnant women too to confirm cancer in the testicles, stomach, pancreas, liver and the ovaries. High levels of AFP can indicate renal cell cancer.
Interpretation of AFP test results: In men and non-pregnant women, the values of the AFP test is 0-6.4 IU/mL (international units per milliliter), 0-20 nanograms per milliliter (ng/mL) or 0-20 micrograms per liter. In pregnant women of about 15 - 22 weeks gestation, the AFP results usually show 19-75 IU/mL, 7-124 ng/mL or 7-124 microgram per liter. AFP test values vary depending on the weight of the woman and race. Black women have higher values than white women and white women have higher values than Asian women. High AFP can suggest multiple pregnancies, fetus with neural tube defects, and abdominal wall defect in the fetus or fetal death. In non-pregnant adults, high AFP values mean cancer in the testicles or ovaries. High AFP can also indicate liver disease and bowel inflammation.
Chorionic Villus Sampling
The diagnostic procedure of taking out a sample tissue (Choroinic Villi) from the placenta to detect congenital abnormalities in a fetus is known as Chorionic Villus Sampling (CVS). With the guidance of ultrasound, the position of placenta is first determined. There are two methods - trans-cervical and trans-abdominal to perform this test. The position of the placenta helps the physician choose a suitable method. For trans-cervical CVS, parameters like the position of the uterus, the size of the gestational sac and the position of the placenta inside the uterus are first determined using abdominal ultrasound. Using a good antiseptic, the vulva, vagina and the cervix are cleansed. The abdomen is also cleansed for trans-abdominal procedure.
Trans cervical procedure: A thin plastic tube is inserted through the vagina and cervix for the trans-cervical procedure to reach the placenta. A tiny sample of chorionic villus tissue is taken out after locating the exact position of the placenta.
Trans-abdominal procedure: This procedure is similar to the earlier one, but a needle is inserted through the abdomen in this test to reach the uterus and then to the placenta. The chorionic villus sample tissue is drawn into the syringe, while the needle is guided by ultrasound.
This sample is then taken to the laboratory for evaluation. This procedure can be conducted even earlier than amniocentesis to detect any congenital defects present in the fetus. It is done at around 10 to 12 weeks after the last menstruation. Study of the DNA, chromosomes and enzymes of the fetus can be conducted using the sample taken out during the test. Results are available within a week or two. If there are any abnormalities found in the fetus, it is easy to conduct a therapeutic abortion, in case it is necessary. Pregnant women over the age of 35 who are at risk for giving birth to a baby with Downs Syndrome or those who have had birth defects in an earlier pregnancy are advised this test. For detecting neural tube defects and the Rh-incompatibility, amniocentesis is a better option. Hemoglobinopathies and Tay-Sachs disease can be detected through Chorionic Villus Sampling.
The risk involved in using CVS is slightly higher when compared to amniocentesis. Some complications like rupture of the amniotic membrane, miscarriage, infection, bleeding, Rh-incompatibility in the mother if she is Rh-negative and contamination of the sample with maternal cells can occur. When CVS is performed after 10 weeks of gestational period, there is a risk for limb defects in the fetus. If the mother's blood is Rh-negative, she has to receive RhoGAM to avoid Rh incompatibility. After the CVS, it is advised to have an ultrasound done after about two or four days to ensure the fetus is fine.
Bibliography / Reference
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