When you are expecting to become a mother, your biggest wish is to have a healthy baby, right? So, today we are going to talk about some special testing methods that help you know in advance whether the baby has any genetic disorders or birth abnormalities while it is still in the womb. We call these `(Prenatal Genetic Testing)`. These tests are not something that everyone should necessarily do, but it is very important for you to be aware of this.
What is this (Prenatal Genetic Testing)?
Simply put, these are tests that can tell if your unborn baby has a genetic disease or birth defect. Unlike the blood type, hemoglobin, and sugar tests you usually get during pregnancy, these genetic tests are not necessary and can be done only if you want . You can talk to your doctor about this and decide which tests are best for you.
Everything in our body is controlled by our genes. These genes are stored in things called chromosomes. So, sometimes, if there are any changes or deficiencies in these genes or chromosomes, various diseases can occur. We call such conditions that are present at birth ``(Congenital Disorders)''. These genetic tests can identify some such conditions even before the baby is born.
What are these two types of tests? (Screening and Diagnostic Tests)
Okay, now let's see. There are two main types of ``Prenatal Genetic Testing''.
1. Screening Tests: These are used to determine if your baby is at risk of having a certain genetic condition. This does not mean that you have the disease. However, if the risk is high, your doctor will tell you what to do next.
2. Diagnostic Tests: These tests can confirm whether or not the baby has a genetic condition. These are usually done only if a screening test shows a risk, or if there is a higher risk for another reason.
Now let's talk about each of these types in a little more detail.
Let's first look at 'Screening Tests' (tests that look for fetal risk)
The most important thing to remember is that these screening tests never say for sure that a genetic condition exists. Even if the result is abnormal, it does not mean that the baby will definitely have the condition. It only means that there is a certain risk compared to others. Your doctor can explain these results to you and explain what steps you should take next. In some cases, they may also recommend a diagnostic test.
There are several types of screening tests:
1. Carrier Screening - Do you have a disease that can be passed on to your baby?
This is a blood test that you and your partner can take. It looks for single-gene conditions that can cause serious health conditions that your baby could inherit. For example, it can detect conditions like Cystic Fibrosis, Sickle Cell Disease, and Spinal Muscular Atrophy.
For example, if your blood test shows that you are a carrier of a certain genetic risk, it is very important for your partner to also get tested. Because, if both parents are carriers of the same genetic risk, the baby is likely to develop a severe form of that disease. This ``Carrier Screening`` test is done only once in a lifetime.
2. Screening for abnormal chromosome number
As we have already said, we inherit chromosomes in pairs - one from our mother and one from our father. Sometimes, during this fertilization process, natural errors can occur. Then parts of the chromosome pair can be either missing or added. For example, ``Down Syndrome`` (the presence of an extra chromosome 21) and ``Turner's Syndrome`` (the presence of an X chromosome missing). The results of these tests can vary from pregnancy to pregnancy.
There are several types of tests:
- Cell-free fetal DNA screening: This is also called `(Non-Invasive Prenatal Testing)` or `(NIPT)`. This involves taking small pieces of your baby's DNA (`fetal DNA`) from your blood and looking for some common chromosomal abnormalities. However, because the amount of this baby's DNA is so small, this test can only be done after 10 weeks of pregnancy.
- Serum screening: This is also a test that takes a sample of your blood. However, it does not directly look at the baby's DNA. Instead, it analyzes the levels of different proteins in your blood to determine your risk of developing chromosomal abnormalities. Examples of these include `(Sequential screening)`, `(Quad screening)` and `(First Trimester Serum screening)`. Each of these tests needs to be done at a very specific time during pregnancy, so it's a good idea to ask your doctor which one is right for you. These tests can usually be done after 11 weeks of pregnancy.
3. Screening for physical abnormalities
Sometimes, chromosomal abnormalities can cause changes in the baby's body structure. Or, even if the chromosomes are normal, the baby may have a physical defect. Ultrasound and blood tests done during pregnancy can give an idea of the baby's risk of developing such physical abnormalities and whether they are due to genetic causes.
- Nuchal Translucency (NT scan): This ultrasound test measures the thickness of the skin at the back of the fetus's neck. If this thickness is too high, it can indicate a risk of chromosomal abnormalities, as well as physical problems such as abnormal development of the baby's heart. This ultrasound is done between 11 and 14 weeks of pregnancy.
- AFP screening (maternal serum screen): A sample of your blood is taken and the level of a protein called AFP (Alpha-fetoprotein) is measured. If this level is too high, it can indicate that there may be some physical problems in the baby's abdomen, face, or spine. This is done between 15 and 22 weeks.
- Quad screen: This measures the levels of four substances in your blood to determine the risk of your baby having chromosomal abnormalities and neural tube defects. This is also called the ``Multiple Marker Screen''. This is also done between 15 and 22 weeks.
- Fetal anatomy scan: This is what many people know as an "Anomaly Scan". In this, an ultrasound is used to examine the baby's body structures, including the developing brain, skeleton, heart, kidneys, abdomen, face, and limbs. This ultrasound is usually done between 18 and 20 weeks of pregnancy.
Important: Again, these screening tests only indicate the possibility of a condition. They do not definitively indicate that a disease is present.
What are 'Diagnostic Tests'? (Tests to find out exactly if there is a disease)
Diagnostic tests can confirm whether a baby has a genetic condition. These tests are only done if the results of a screening test are abnormal, or if you have other reasons to think your baby is at higher risk of having a genetic condition (for example, someone in your family has the condition).
The two most common types of diagnostic tests are `(Amniocentesis)` and `(Chorionic Villus Sampling / CVS)`.
- Amniocentesis: In this test, the doctor inserts a small needle through your skin into your uterus and takes a small sample of the amniotic fluid that surrounds your baby. This test is done between 16 and 20 weeks of pregnancy.
- Chorionic Villus Sampling (CVS): In this test, the doctor inserts a needle into the uterus and takes a small sample of cells from the placenta. The doctor will decide whether to insert the needle through the abdomen or through the vagina, depending on which is safer. The CVS test is done between 11 and 13 weeks of pregnancy.
The samples are then sent to a laboratory for analysis. The laboratory can perform special tests such as Fluorescence In Situ Hybridization (FISH), standard Karyotyping, and Microarray. Some diagnostic tests can provide results in as little as 72 hours, while others can take more than two weeks.
Should these genetic tests be done? Who should do these?
Whether or not to undergo this ``Prenatal Genetic Testing'' is entirely your personal decision. If you are unsure, you can ask your doctor what he or she recommends. The results of these tests can provide very important information about the health of the baby. Usually, all pregnant women are informed about these genetic screening tests as part of their prenatal care.
Some reasons why some families decide to have diagnostic tests are:
- Receiving an abnormal result from a screening test.
- Having a family history of a genetic condition.
- Pregnancy over the age of 35.
- Having had a previous miscarriage or stillbirth.
Is it necessary to have these tests during pregnancy?
No, it is not necessary. It is a decision based on your personal beliefs and medical history. Some parents like to know in advance if their baby will be born with a certain condition. This allows them to plan for their baby's care in advance. Unfortunately, some families may have very sad outcomes, and they may have to make the difficult decision of whether to continue the pregnancy. So, whether or not to have this screening or diagnostic test is entirely up to you and your doctor.
How are these tests done?
Most `(Prenatal Genetic Screening)` tests are done on a blood sample from the pregnant mother. If the screening test results show that there is an increased risk of a birth defect, the doctor may do more in-depth tests (``invasive tests``) to identify specific conditions. These in-depth diagnostic tests are ``(Amniocentesis)`` and ``(CVS)``.
What tests are done at different weeks of pregnancy?
This is also a problem for many people.
First Trimester (within the first 3 months) tests
The first trimester serum screening, cell-free fetal DNA screening (NIPT), and NT ultrasound are all done between 11 and 14 weeks of pregnancy. By combining the information from these blood tests and the ultrasound, you can get an idea of the risk of common chromosomal disorders such as Down Syndrome.
``Carrier screenings`` can be done at any time during your pregnancy, even as early as 6-10 weeks. These tests look for ``single gene`` conditions that you can pass on to your baby. However, ``Carrier screenings`` cannot detect conditions caused by chromosome abnormalities, such as ``Down Syndrome``.
Cell-free fetal DNA testing (NIPT) tests the baby's DNA in your blood. It looks for chromosomal conditions such as Down Syndrome, Trisomy 13, and Trisomy 18. This test can be done as early as 10 weeks of pregnancy, or later in the pregnancy.
Second Trimester (between 4-6 months) Tests
Second trimester screening tests are done between 15 and 22 weeks of pregnancy. The blood tests done at this time are the `(Maternal Serum Alpha-Fetoprotein / AFP screen)` and the `(Quad screen)`. The `(Quad screen)` gets its name because it measures four types of proteins (`Alpha-fetoprotein / AFP`, `Estriol`, `Human Chorionic Gonadotropin / hCG` and `Inhibin-A`). These tests help your doctor determine if your baby is at increased risk of having genetic or physical abnormalities. `(Fetal anatomy ultrasound)` (Anomaly scan) is another screening method that can look for genetic or physical abnormalities in your baby.
Can these 'screening' tests for conditions like Down Syndrome be wrong?
Yes, there is always a chance that a screening test will be wrong. That is, sometimes there may be a risk even though it says there is no risk, and sometimes there may be a risk even though it says there is no risk (this is called `false positive` and `false negative`). Your doctor can explain the accuracy rates (`accuracy rates`) of any screening test you have during pregnancy.
Are there any risks with these tests?
Screening tests (taking a blood sample) are not considered to be risky. However, if you go for a diagnostic test like ``Amniocentesis`` or ``CVS``, there is a very small risk . Those risks are infection, bleeding, or miscarriage. That is why these diagnostic tests are not done for everyone in general ``Prenatal Genetic Screening``, but only for those who are especially suspicious.
How long does it take for the results to come back? What do the results mean?
Screening tests take a few days to get results. Diagnostic tests can take a few days to a few weeks to get results. Most of the time, these samples are sent to a lab for testing. Your doctor will get the results first, and then they will tell you the results.
Screening test results only indicate risk. They do not tell you for sure whether the baby has a genetic condition.
- If a positive result is obtained, it means that the baby is at a higher risk of developing that disease than the general population.
- If a negative result is obtained, it means that the baby has a lower risk of developing that disease than the general population.
Your doctor may suggest a diagnostic test, such as a CVS or an amniocentesis. Or, they may refer you to a genetic counselor, who specializes in high-risk pregnancies and genetic conditions. Don't be afraid to talk to your doctors about what your test results mean and the risks and benefits of diagnostic tests.
Can the baby's gender be determined through these tests?
In addition to providing information about the risk of genetic conditions, the ``Cell-free DNA screening / NIPT'' test can also provide information about the sex of the baby. ``Ultrasound'' can also sometimes determine the sex. However, this is only an additional benefit, not the main reason for the test.
What should I ask the doctor about these genetic tests?
Screening and diagnostic tests during pregnancy are personal decisions. You may have questions about which screening tests you should have or what your test results mean. Don't be afraid to ask questions. Remember, only you and your family can decide how to deal with positive results from both types of genetic tests.
Some common questions you can ask:
- "What screening tests do you recommend based on my health history?"
- "If my screening test result is `Positive`, what are the next steps?"
- "Can these genetic tests harm the baby?"
- "What are the chances of false positives?"
Finally, things for you to remember (Take-Home Message)
There is no right or wrong answer to Prenatal Genetic Testing. The decision is up to you and your family. If you have concerns about these tests, or if you want to understand what each test will look for, talk to your doctor. He or she can discuss the risks and benefits of each genetic test with you and help you make the best decision for you and your family.
Remember, most babies are born healthy. However, it's important to understand what your options are and what genetic tests are available to you. Your doctor is your best guide on this journey.
` Pregnancy, genetic testing, baby health, fetal testing, screening tests, diagnostic tests, Down syndrome, ultrasound
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