Prenatal testing is a way of giving your baby a check-up while it is still growing in your uterus. There are a wide variety of highly sensitive tests available that pick up chromosomal abnormalities, other birth defects and genetic diseases. Not all tests are appropriate for everyone.
When to Prenatal Test
Tests Available at UT Medical Center
When You Should Consider Prenatal Testing
Generally, your doctor will recommend the prenatal tests he thinks are right for you. Here are some of the most common factors that affect your physician's decision on what to recommend.
- Your age—If you're over 35, your doctor may recommend extra tests to make sure the baby is developing as it should.
- Your past pregnancy history—If you have had one or more miscarriages, your doctor may recommend extra tests.
- Your medical history—Some chronic conditions such as diabetes make pregnancy riskier. For this reason, extra tests may be recommended.
- Both parents' genetic background.
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If a genetically linked disease is present in either parent's family, you may want to undergo extra prenatal testing. Some genetic diseases include the following.
- Huntington's disease
- Cystic fibrosis
- Tay-Sachs disease
About 97 percent of women who undergo prenatal tests get good news—so having prenatal tests can be tremendously reassuring. Ultimately, however, the decision of whether to undergo prenatal testing is up to you and the baby's father. Here are issues to consider when you discuss prenatal testing with your physician.
- Your options if the baby has a serious birth defect or genetic disease.
There is very little doctors can do while the baby is still in utero to treat most birth defects or genetic diseases. Discuss your options carefully with your doctor and the baby's father before deciding whether to test for these problems.
- What to test for.
Do you want to know everything the test can tell you? This includes your baby's gender. Sometimes, there's a specific risk factor that helps you determine what you want to test for, but since prenatal tests can pick up hundreds of disorders, it is important to discuss this in advance.
- Risks of the tests.
Although most prenatal tests are considered very safe, there are some risks.
For more details about these risks, see below. It is important that you discuss the risks with your doctor so that you can make informed decisions.
^ Top Tests Available At UT Medical Center
There are a wide variety of prenatal tests available at UT Medical Center. Its doctors and caregivers make sure that your tests are performed to the highest degree of accuracy possible, providing counseling before the tests to help you understand the possible risks and afterwards to help interpret the results. Here are some of the prenatal tests offered at UT Medical Center.
Ultrasound
Expanded alpha-fetoprotein (X-AFP) screening test
Amniocentesis
Percutaneous umbilical blood sampling (PUBS)
Chorionic villus sampling (CVS)
Ultrasound
Ultrasound, one of the most common tests, uses a high-frequency sound wave to produce pictures of the fetus on a TV monitor. This non-invasive, painless test safely has been used for more than 25 years and has no side effects. Ultrasound can be used at any time throughout the pregnancy for a variety of reasons.
- Dating the pregnancy
- Determining the baby's gender and size
- Confirming a multiple pregnancy (i.e., twins, triplets, etc.)
- Determining the amount of amniotic fluid and size of placenta
- Viewing the baby's basic anatomy
- Diagnosing certain birth defects, including neural tube defects such as spina bifida, structural abnormalities and heart defects
If an ultrasound test detects a potential problem, it usually is followed by another, more sensitive test.
^ Available Test Menu Expanded alpha-fetoprotein (X-AFP) screening test
Alpha-fetoprotein (AFP) is a chemical produced by the fetus and passed into the mother's bloodstream, where it can be measured by a simple blood test. The test usually is performed 15 to 20 weeks into the pregnancy. An unusually high or low level of AFP in the mother's blood may indicate a risk one of the following problems or conditions.
- Multiple pregnancy (i.e., twins, triplets, etc.)
- Neural tube defects such as spina bifida
- Down's syndrome or other chromosomal disorders
The X-AFP test lets your doctor know that more tests may be needed. However, it indicates risk only-not a diagnosis. In fact, of 50 women with an abnormal X-AFP test, only one or two are carrying babies with serious problems.
During amniocentesis, a long, thin needle is inserted into the uterus to remove a small amount of amniotic fluid, which contains a few fetal cells. Early amniocentesis can be performed at 12 to 13 weeks, while traditional amniocentesis is performed at 16 to 18 weeks. The fetal cells contained in the fluid are then tested for the following.
- Genetic diseases
- Chromosomal disorders, including Down's syndrome and sex-chromosome abnormalities
- Single gene defects, including spina bifida
- Neural tube defects
Amniocentesis is most commonly offered to women older than 35 and women who have given birth to a child with chromosomal disorder or have a family history of such disorders and couples who have a family history of genetic disease.
There is a small risk of miscarriage with this procedure (fewer than one in 200). Test results are back within two to three weeks.
^ Available Test Menu Percutaneous umbilical blood sampling (PUBS)
PUBS is a test of blood from the umbilical vein of the umbilical cord. Most commonly performed in the third trimester, PUBS tests for chromosomal disorders or fetal blood problems. To draw the blood, a needle is inserted into the mother's abdomen. PUBS is not as common as amniocentesis-but it is faster. Your doctor might recommend PUBS over amniocentesis if
- There are signs that the baby has a fatal chromosomal disorder and is in distress.
- Your doctor suspects that the baby might be anemic-blood sampling is the only way to confirm this. If the baby is anemic, the needle used to draw the blood remains in place for a transfusion.
CVS tests for many of the same disorders that amniocentesis does, but it is performed earlier in the pregnancy, about 10 weeks or possibly sooner. CVS tests a small piece of the placenta, which can be removed through the mother's abdomen with a needle or through her cervix with a catheter.
The chief advantage to CVS is that it can be performed so early into the pregnancy that if there is a problem, you have more time to consider your options. It is a good choice for women at higher risk for birth defects or who need results quickly. However, there are some disadvantages, including the following.
- The risk of miscarriage is higher than with amniocentesis.
- There is a slight risk of interuterine infection.
- It is not as accurate as amniocentesis.
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