Genetic Testing during Pregnancy – Purpose, Types & Accuracy

You may have to undergo various tests and screening during pregnancy to ensure your baby’s well-being. Sometimes parents may be advised for genetic testing during pregnancy, this may be performed to overrule any genetic abnormalities in the unborn baby. In the following article, we shall be discussing the purpose, types and various other aspects of genetic testing.

What is Genetic Testing?

Genetic testing involves testing the blood of both the parents to look out for abnormal genes, which the parents may pass on to their baby. In case one of the parents has abnormal genes, there may not be any genetic complications. In case both the parents have an abnormality in their genes, even then there is only a 25 percent chance that your baby may have faulty genes too.

When is Genetic Testing Ideally Done in Pregnancy?

It is recommended that genetic testing should be done before you plan to get pregnant. And where the pregnancy may be unplanned, it is recommended that you opt for genetic counselling at the earliest.

Why is This Testing Recommended?

You may be advised genetic baby testing or genetic foetal testing by your doctor because of any of the following reasons:

• If you are a woman who has had two or more than two miscarriages. Sometimes, certain chromosomal deformities in the foetus may lead to a spontaneous miscarriage.
• If you, your partner or a close relative has some kind of genetic disorder.
• If you already have a child who is suffering from birth defects (due to genetic reasons).
• If you are an older woman, 35 years or more then genetic testing for pregnancy over 35 may be recommended.
• If you have had a stillbirth with your baby having prominent physical signs of genetic illness.
• If the prenatal screening results were abnormal.

These are some of the reasons for which your doctor may recommend you to go in for genetic testing.

What Are Common Genetic Diseases

Here are some common genetic diseases that may occur due to faulty or deformed genes:

1. Thalassemia

Thalassemia is a blood disorder which may lead to complications like anaemia, liver ailments or problems in bone growth. In some cases, if a baby has this genetic disorder, he may not even survive.

2. Cystic Fibrosis

Cystic fibrosis is a fatal genetic condition that may cause life-threatening complications in your baby. It may cause severe digestive problems or may even lead to lung damage.

3. Sickle Cell Disease

This genetic problem may lead to various health complications such as anaemia, weakened immune system etc.

4. Fragile X Syndrome

This may lead to mental retardation, learning disabilities and developmental complications in your child.

5. Tay-Sachs Disease

This genetic disorder adversely affects the nervous system of your baby and thus, may lead to various problems of the nervous system, especially during early childhood.

6. Duchenne Muscular Dystrophy

This genetic disorder becomes prominent before your child may begin his formal education, which is around 6 years of age. This may lead to weaker muscles and may also cause fatigue; it may progress from the legs to the upper part of the body.

Main Types of Prenatal Genetic Tests Performed during Pregnancy

You may wonder what genetic testing is done during pregnancy? Well, there are two main tests that your doctor may recommend, screening tests and diagnostic tests. Here is more information on how these prenatal genetic tests may be performed during pregnancy to check for any genetic glitches:

1. Screening Tests

The screening tests may tell if you have a baby with genetic ailments.

a. First Trimester Combined Screening Test

Genetic testing during pregnancy first trimester is done through blood tests during your 10 to 12 weeks of pregnancy which may also include an ultrasound at around 11 to 13 weeks of pregnancy. The results of both these tests may help in establishing the risk of trisomy 21 (Down syndrome) or trisomy 18. However, the tests do not tell whether or not your baby may have these ailments.

b. Maternal Serum Screening

For genetic testing during pregnancy second-trimester, blood test may be conducted around 15 to 20 weeks of pregnancy to establish the risk of neural birth defects (spina bifida), Down syndrome or trisomy 18. In case you are at risk, you may be recommended to go for further tests.

2. Diagnostic Tests

The diagnostic tests may tell you about the defects that your baby may have.

a. Chorionic Villus Sampling (CVS) (11 to 12 weeks)

This test involves taking a sample of the placenta and testing it for any genetic diseases such as cystic fibrosis, Down syndrome and others. In some rare cases, a woman may have a miscarriage due to this test, though the chances are only 1 in a hundred.

b. Amniocentesis (15 to 18 weeks)

This test involves testing the amniotic fluid to check for any genetic disorders such as Down syndrome and others. Sometimes this test may lead to a miscarriage, though the chances are very minimal (1 in every 200 cases).

c. Ultrasound Scans (18 to 20 weeks)

This test may be done at a bit later stage in pregnancy to identify structural and physical abnormalities, limb defects, heart abnormalities and spina bifida.

What Do the Results of Prenatal Genetic Testing Mean?

The test results of the prenatal genetic testing can be positive or negative. If the test results are positive this means that your baby may be at a higher risk of having various genetic abnormalities but that does not mean that your baby will definitely have them. On the other hand, if the test results are negative then it means that your baby has low chances of having any genetic diseases; however, it does not entirely rule out the possibility.

The genetic testing that involves amniocentesis or Chorionic Villus Sampling, may give you more comprehensive and definite results in comparison to other testing methods. After your test results, your doctor may guide you to take help of a genetic counsellor in understand your case and also on the further course of action.

How Accurate Are These Genetic Screening Tests?

Just like the possibility of any test results going faulty, there are chances that genetic screening tests may show faulty results too. If the tests results are positive but there is not any problem, then it is called false-positive test results. Whereas, if the test results are negative but there is a problem, then it is called false-negative test results. You may get in touch with your doctor to know more about your test results and their authenticity.

Are there Any Risks of Genetic Testing While Pregnant?

Pregnancy may make you sceptical because everything that you do may have an impact on your baby too. So, you may wonder are there any genetic testing pros and cons that you should know about. The first and foremost thing to understand is that genetic testing is a personal choice. So, if you are thinking whether or not genetic counselling have any risk, the answer is that it may have more emotional stress rather than physical stress. Because it can be extremely disheartening and difficult to know that you may have a baby with a genetic disorder, which may adversely affect your child’s life.

Also, the screening tests only tell you whether you at a risk of having a baby with a genetic disorder and to know defects you will have to undergo diagnostic tests. Where some parents may want to know about a genetic disorder to prepare better for their baby, on the other hand, others may want to know to terminate the pregnancy. However, there are some parents who do not want to know whether or not their baby may have any genetic disorder. It is entirely up to you as a parent to decide, if you want to go in for genetic counselling or not.

If you wish to go for genetic testing or not, it is absolutely your decision to make. However, if you think you may or your partner may have any kind of genetic disorder, then it will be a good idea to talk to your doctor about the same and know what best you can do to avoid complications in your baby.