Ultrasound
This is a technique that uses sound waves to take a picture of the baby in the womb. It is used to locate the position, size and structure of the fetus and placenta in the womb. It is valuable in determining the age of a fetus and can detect multiple pregnancies as well as many malformations such as spina bifida, and various heart or kidney problems. Because it uses sound waves instead of radiation, ultrasound is safer than X-rays. It works by bouncing sound waves off the developing fetus. Echoes from the waves are converted into an image on a TV monitor. Ultrasound may be used to help perform other prenatal diagnostic tests. If amniocentesis or CVS are called for, doctors are guided by ultrasound in removing cells to test for certain possible birth defects. For pregnancy scanning, sound waves are usually sent by a hand held device rubbed back and forth across the pregnant woman’s abdomen. Depending on the position of the fetus and the purpose of the ultrasound, the procedure may take as long as an hour. Information obtained using ultrasound is often used to alter prenatal care to improve the chances to deliver a healthy baby. Ultrasound and other prenatal tests can let a woman know if her baby has certain birth defects or other special risks. Knowing about the problems before birth provides time to plan the baby’s treatment if needed.
CVS
Chorionic villus sampling is a prenatal test that can diagnose or rule out certain birth defects. The test is generally performed about the 10th or 11th week of pregnancy. CVS is not routinely offered to all pregnant women because the test carries a risk of miscarriage, and possibly other complications. CVS may be offered when there is an increased risk of chromosomal or genetic birth defects and parents would like test results as early in pregnancy as possible. CVS requires taking a small piece of the chorionic villi. Either a needle is inserted through the abdomen or a slim tube is inserted through the vagina to take a tiny tissue sample from outside the sac where the baby develops. The tissue is analyzed for chromosome disorders or various genetic conditions. Results are usually ready in one to two weeks. CVS tests are slightly less accurate than amniocentesis for chromosome analysis, and the risk of miscarriage is higher— one in 50 to 100.
Amniocentesis
This is one of the best-known prenatal diagnostic techniques for certain congenital disorders. It is usually performed between the 13th and 15th weeks of pregnancy. In this procedure, a thin, hollow needle is inserted into a woman’s uterus through the abdomen, guided by ultrasound used to view the fetus. The technician draws out some fluid surrounding the fetus. Fetal cells floating in the fluid can be analyzed to detect chromosomal abnormalities, more than 100 metabolic disorders and some anatomic defects. There is low risk (less than one in 200) of miscarriage or infection following the procedure. Results of the test are ready in one to three weeks.
Alpha-Fetoprotein Screening
This blood test is most often done between 16 and 18 weeks. The results are usually available within a week. The test identifies pregnancies at higher-than-average risk of certain serious birth defects, such as spina bifida and Down syndrome. The test can provide information about a developing fetus. In most cases, an abnormal test result does not indicate a problem with the fetus. Alpha-fetoprotein(AFP) is a substance produced by the liver of the fetus. A small amount of AFP passes into the mother’s bloodstream, where the concentration rises gradually. AFP levels can be measured during pregnancy by taking a sample of either the mother’s blood or the amniotic fluid. If the test levels are abnormal, the test may be repeated. This test cannot diagnose a birth defect, it can only indicate an increased risk. Neural tube defects are among the most common and severe problems associated with high test levels. Low test level results are sometimes associated with chromosomal abnormalities, such as Down syndrome. However, for the majority of women, this test provides reassurance that their fetus does not appear to have certain serious birth defects.
Umbilical Vein Sampling
(Cordocentesis) In this procedure a fine needle is passed through the mother’s abdomen into the fetal vein in the umbilical cord. The technique allows fetal blood to be tested, facilitates intrauterine blood transfusions, and enables drugs to be injected directly into the baby if necessary