Pregnancy is a period that makes you think about lots of things. Among the things you think about are: choosing a name for the baby, buying her clothes and baby furniture for her room, and the changes that her presence will bring into your life. All this puts a smile on the face of expectant mothers. Still, some thoughts cause a lot of fear, such as thinking about possible genetic defects in your baby.
Among these defects or genetic diseases, Down syndrome, Cystic Fibrosis, and Neural Tube Defects can be mentioned. But what is pregnancy genetic testing good for? There are many pregnancy genetic tests (prenatal screening tests) to identify possible problems and conditions and later diagnose and treat such cases. This article discusses the types of genetic tests during pregnancy, when they should be performed, and the technologies used to perform them.
Definition of Genetic Tests
We can define genetic tests as follows: Types of tests performed primarily to check the possibility of your child suffering from genetic problems and to put an exact diagnosis in place if the initial results are positive. In fact, the second round of tests helps doctors to accurately diagnose and determine the details of the problem. If such problems are not prevented, they may lead to birth defects.
These tests are common in the first and second trimesters of pregnancy. Interestingly, the third type of such test is performed before pregnancy. The test is called Carrier Screening and is helpful as a genetic test before pregnancy. You will usually hear about genetic tests in the first session when you visit the doctor for a prenatal appointment.
You need to know that genetic testing in pregnancy is not mandatory and depends entirely on your personal decision. But in some situations, it is better to do them. For example, when:
- The mother's age is over 35 years.
- In the previous childbirth, her child was diagnosed with special genetic conditions.
- A history of genetic disorders runs in the mother's or her partner's family.
However, a more critical point is that the results of genetic tests are not definitive, especially the tests performed in the first round. That is, the first round of tests is done only to determine the probability of specific problems (such as Down syndrome or Syndrome Trisomy 18) in your baby. That is because these tests can miss something or show a result that is not correct. These tests are noninvasive and optional, but most likely, your doctor will recommend you to do them.
Another category of prenatal testing is the tests performed to check the general conditions of the mother and her baby. As an example, we can refer to the glucose tolerance test. As can be guessed from its name, this test measures the amount of sugar in the mother's blood to check for the possibility of gestational diabetes.
Of course, there is also a third group of genetic tests the doctor may ask you to perform depending on certain conditions. For example, your race, ethnic group, or living conditions (like living in a region or city where a particular disease has been prevalent) may be considered by your doctor when ordering further genetic tests.
Especially if you think of getting pregnant soon, it is a good idea to go for receiving genetic counseling offered by a genetic counselor. She may write you some diagnostic tests or advise you to do prenatal genetic testing.
Now we will check the genetic tests advised as regular trimester screening based on every trimester of pregnancy:
Genetic Tests In The First Trimester of Pregnancy
These tests can be started from the 10 weeks of pregnancy and include routine blood tests and ultrasounds, so they are classified as noninvasive tests. Due to the baby's position in the first weeks of growth and formation inside the mother's womb, these tests check the general state of the baby's development, growth rate, and general health conditions.
Among the problems that may occur during the first trimester screening of pregnancy, we can point to Cystic Fibrosis, heart problems, or Down Syndrome. Thus, genetic testing during pregnancy's first trimester is suggested by most OBs.
For example, to diagnose Down's Syndrome, a Nuchal Translucency Ultrasound is used to collect some fluid from the back of the fetus's neck and measure it. If its amount is higher than normal, your child may be at risk of developing this syndrome.
Blood tests performed at this time of pregnancy aim to check plasma protein A and a specific human hormone. In general, your doctor wants to see if there are any signs of mom having HIV, Hepatitis B, Syphilis, or severe anemia. Therefore, the blood test is taken to measure the said protein and hormone levels in your blood.
But the most specialized genetic test in the first trimester of pregnancy is called CVS or Chorionic Villus Sampling, which is done by sampling the placenta. Your doctor might request it if a sign of a problem has been detected in earlier tests. This test is performed in two ways: abdominal and cervical.
But, the happy news is that you may be able to know the gender of your child through a test called a Noninvasive Prenatal Test (NIPT)! This is also a screening test performed in pregnancy.
Genetic Tests in The Second Trimester of Pregnancy
Second-trimester genetic tests, including blood tests and ultrasound, are performed between 14 and 18 weeks of pregnancy. Ultrasound during the second trimester of pregnancy is also called a Fetal Anatomy Survey.
By taking a blood test, your baby will be rechecked for the possibility of Down syndrome; another possible problem during pregnancy is Neural Tube Defects. Of course, the blood test of the second trimester of pregnancy or Quad Marker Screening is usually done if you have not done it in your first trimester.
Gestational diabetes is another danger threatening mothers and their children during pregnancy, delivery, and after childbirth. Usually, mothers with diabetes will have children of a larger size than usual, which increases their risk for Cesarean Section.
The fourth genetic test of the second trimester of pregnancy is called Amniocentesis, which is usually performed after 15 weeks of pregnancy. Using this test, your doctor checks some of the amniotic fluid inside the uterus for possible Down Syndrome or Spina Bifida. This test is performed if your doctor deems it necessary due to the presence of certain conditions that we mentioned above in the Definition of Genetic Tests section.
How to Interpret The Results of Genetic Tests
Combining the results of the tests you gave in the first and second trimester of pregnancy to identify genetic and chromosomal disorders gives more accurate results. Of course, in this method, you must wait until the second trimester of pregnancy to interpret the results.
In addition to the tests we mentioned, there is also a cell-free DNA test you can take. It is a type of blood test to check whether the fetus has a range of disorders like Patau Syndrome, Down Syndrome, Edwards's Syndrome, or problems related to the number of sex chromosomes. If the initial test results are positive, a CVS test will follow.
Doing or not doing genetic tests is entirely voluntary. But suppose some special conditions apply to you, such as having a child with genetic problems, the presence of a defective gene in the family of the mother or partner, or pregnancy at an advanced age. In that case, it is better to do these tests.
Genetic pregnancy tests are performed in the first and second trimesters. Their purpose is primarily to check the possibility of potential risk for your baby and then check the positive results more closely. These tests may be invasive or noninvasive, and interpreting their results together is more meaningful.