What is a genetic diagnostic test for pregnant women?
Genetic diagnostic test is a test carried out by analyzing samples from blood or tissue. This test will inform you whether you, your partner, or your baby has a gene inherited which causes abnormalities.
Difference between genetic diagnostic test and screening test
Please note that screening tests and diagnostic tests are two different things. Screening tests are done by ultrasound, blood test, or both. A diagnostic test is a test that involves inserting a needle into the area associated with pregnancy.
The advantage of a screening test is that the test does not pose a risk of miscarriage in your pregnancy, and the test also provides information about the possibility of your child being born disabled. The disadvantage of a screening test is that the test cannot provide a definite answer between yes or no about whether your child will be born disabled. In addition, screening tests only provide information about certain disorders. Screening tests are done only to predict more accurate risks about the possibility of your child being born disabled, not to diagnose it. Most pregnant women usually do a screening test to determine whether they should continue further tests, such as genetic diagnostic testing.
The advantage of genetic diagnostic tests is that this test will diagnose abnormalities in your child. In other words, this test can provide a definite answer between yes or no about your child's abnormality. The disadvantage of the genetic diagnostic test is this test (although it is less likely) can cause miscarriage.
When do pregnant women need to do a genetic diagnostic test?
- You and your partner want to start building a family, but one of you or your closest relative has a hereditary disease.
- You already have a previous child who was born with a disability. But keep in mind, not all children born with disabilities occur because of abnormalities in the genetic makeup. It could also be that the child is born disabled because of exposure to poisons, infections, or physical trauma before birth. Even sometimes, the reason for a child born with a disability is unknown. It is probable that the disability is not inherited.
- The mother has had two or more miscarriages. Some chromosomal abnormalities in the baby can cause miscarriages. Having a miscarriage several times can lead to genetic disorders.
- The mother has given birth to a stillborn child with physical signs involving genetic disorders.
- The pregnant woman is more than 34 years old. The possibility of having children with chromosomal abnormalities increases with the age of pregnant women
- The results of the screening test give abnormal results. If the results of a screening test indicate a possible genetic abnormality, the doctor may recommend doing a genetic diagnostic test.
Pros and cons ofdiagnostic testing
By doing this genetic diagnostic testing, of course parents will get information in advance about the possible abnormalities that the child might experience. This information is useful for parents to prepare what is needed for their children who might have special needs. However, the positive results of the genetic diagnostic tests of course cannot change. Parents need to ask themselves whether if later the results of this genetic diagnostic test will make them feel worried about continuing the pregnancy, or even to calm their hearts, the couple decides to abort it because the diagnosis is obtained from the test results.
Types of genetic diagnostic tests
Chorionic villus sampling (CVS)
CVS is a diagnostic test that is usually done in the first trimester of pregnancy, approximately between 10-13 weeks of pregnancy. The main purpose of CVS is usually to determine whether the baby has a normal chromosome number (46 chromosomes). So, CVS is usually done to determine genetic abnormalities in infants such as Down syndrome, trisomy 18, trisomy 13, and other abnormalities caused by abnormal chromosomes. CVS can also be used to look at the genetic risk conditions in your baby that might be caused by heredity or the results of carrier screening.
There are two ways to do CVS, either by inserting a needle through the mother's stomach or through the cervix to the placenta. A small portion of the placenta will then be taken and taken to the laboratory for genetic testing. Results from CVS usually come out after about 1-2 weeks after the action.
The risk of CVS is that the mother has a miscarriage. But the chances are very small, about 1 in 250 babies or 1 in 300 babies. Pregnant women who undergo CVS need to undergo a blood test in the second trimester of pregnancy to evaluate the risk of the baby experiencing congenital defects due to incomplete neural tube during embryo growth.
Amniocentesis is a diagnostic test that is usually done in the second trimester of pregnancy, approximately between 15-18 weeks of pregnancy. However, this test can be done at any time during pregnancy. The purpose of this Amniocentesis is actually similar to CVS, which is to determine whether the baby has a normal chromosome number (46 chromosomes). So, Amniocentesis is also done to determine genetic abnormalities in babies such as Down syndrome, trisomy 18, trisomy 13, and other abnormalities caused by abnormal chromosomes. Amniocentesis can also be used to look at genetic risk conditions in your baby that may be caused by heredity or the results of carrier screening. The difference with CVS, Amniocentesis is also commonly done to see if there is a possibility the baby has a congenital defect due to incomplete neural tube during embryo growth.
Amniocentesis is done by inserting a needle through the mother's stomach into the amniotic water where the baby is in the womb. About 3 spoons of amniotic water are taken with a needle with guidance from USG. In the amniotic fluid there are baby cells, which later this cell is used in the laboratory for genetic testing. The risk of having a miscarriage after doing Amniocentesis is much smaller than CVS, about 1 in 500 babies to 1 in 1000 babies.
Before you do CVS or Amniocentesis, you must meet a genetic counselor to see a history of your family's abnormalities and also the details of the procedure to be undertaken. You will be referred to an ultrasound, where a specialist maternal fetal medicine (MFM) will take CVS or Amniocentesis. After CVS or Amniocentesis, you are allowed to go home or continue to work. However, you are advised to avoid strenuous activities during the first 24 hours.
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