Genetic tests during pregnancy

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So many things happen to your body during pregnancy. You may be wondering what your baby will look like or what stage of development he is in. Most pressing of all, you may wonder if all is well in there.

Genetic testing gives parents (and doctors) insight into your baby’s development. It also helps determine genetic issues that need attention during or after your pregnancy. Here’s what you need to know about these tests, what the different types are, and when they’re typically done.

Once the initial excitement of seeing your positive pregnancy test wears off, you will need to schedule your first prenatal appointment. Over the next 9 months, your doctor will suggest various tests that will assess your health and that of your baby.

Some tests are meant to look for genetic problems or other health issues your baby may have. The idea is that with this information, you can get proper medical care and feel informed about your child’s potential health complications.

Some tests are suggested for everyone during pregnancy. Others may be based on other factors, such as your age, ethnicity, or family medical history. That said, genetic screenings or tests are optional during pregnancy.

There are two classifications of prenatal genetic testing. The main difference between the two is that one type assesses the possibility of problems while the other gathers more detailed and definitive information for diagnosis.

Screening

Screening tests are in general non-invasive – for example, blood tests or ultrasounds – and provide results that may indicate that a baby has the potential for certain health problems or birth defects.

These tests do not provide a diagnosis or confirm a diagnosis. In fact, drug tests may show that there is a potential problem when there really isn’t. Alternatively, drug tests may miss problems that are actually there.

Diagnostic

Diagnostic tests are in general more invasive – for example, collecting pieces of placenta – and can provide definitive results on health problems or birth defects.

Diagnostic tests are often offered to women over 35, those with a history of birth defects, or those with certain health conditions, such as diabetes, lupus, or high blood pressure.

Screening tests usually give a positive or negative result for certain conditions or birth defects. They indicate the potential for problems with a confirmed diagnosis.

Screenings can be done in the first or second trimester.

First trimester genetic screening tests

The following screening tests are done together sometimes between weeks 11 and 13 during pregnancy.

  • Maternal blood screening: These blood tests can detect levels of human chorionic gonadotropin (hCG) and plasma pregnancy-associated protein A (PAPP-A). Very down or very high levels of these proteins can indicate that a baby has a chromosomal disorder.
  • Ultrasound: This imaging test – also called nuchal translucency (NT) ultrasound – is done by placing a probe on the lower abdomen (abdominal ultrasound) or inserting it into the vagina (transvaginal ultrasound). He takes pictures of the developing baby and looks for fluid behind the baby’s neck. If there is excess fluid, it may indicate that the baby has a chromosomal problem or a congenital heart defect.

Second Trimester Genetic Screening Tests

  • Maternal serum screening: This screening involves a blood test that looks for markers of trisomy 21 (Down’s syndrome), trisomy 18 (Edwards’ syndrome) or neural tube defects. For the most accurate results, this test should be administered between weeks 15 and 17, but it can be performed anywhere between 14 weeks and 20 weeks, 6 days.
  • Abnormal ultrasound: This ultrasound examines your baby from head to toe. Your healthcare provider will review your baby’s head size and other potential physical issues. This ultrasound is usually performed between weeks 18 and 20 and, yes, it is also the scanner where you can find out the sex of your baby.

Combined first and second trimester screening

Instead of taking results from just one screen, your doctor may suggest collecting a combination of first-trimester and second-trimester screen results. Combining the information from these screens can give you a more accurate result than using just one screen.

Other genetic screening tests

  • Cell-Free DNA Genetic Screening Tests: Also called non-invasive prenatal testing (NIPT), cell-free DNA genetic screening tests involve a simple maternal blood test that looks for genetic information from the baby’s genetic material circulating in the mother’s blood. This screening can look for Down syndrome, Patau syndrome, Edwards syndrome, and sex chromosome problems. It can also show the gender of the baby. Cell-free DNA screenings can be done after week 10 of pregnancy.
  • carrier test: Another screening can be done even before becoming pregnant. This is called the carriage test and it is for couples who are worried about certain inherited genetic disorders they may have in their family. This test can be done any time before pregnancy and is usually done by taking blood or a tissue sample from the cheek.

Genetic testing during pregnancy involves testing cells from the placenta or chorionic villi. Various technologies are used to test these materials, including:

  • Karyotyping: Karyotyping consists of classifying the chromosomes from largest to smallest. This way any missing, extra or damaged chromosomes are more easily sorted out. The results take between 1 to 2 weeks.
  • Fluorescence in situ hybridization: Also called FISH, this method detects missing/extra chromosomes for trisomies 13, 18 and 21 as well as X and Y chromosomes. Results only take 1-2 days.
  • Analysis of chromosomal microarrays: This method searches for missing/extra chromosomes in sets of chromosomes. It can detect problems that karyotyping misses and takes about 1 week.
  • DNA test: You can also request specific DNA tests if you or your partner have a family medical history of certain conditions, such as cystic fibrosis or other genetically inherited health conditions.
  • Amniocentesis: Amniocentesis is performed between the 15th and 20th week of pregnancy. However, your doctor may suggest this diagnostic test any time before birth, depending on the circumstances. To perform the test, your doctor inserts a thin needle into the uterus to collect a small amount of amniotic fluid for analysis. The needle is guided using ultrasound technology for added safety. Risks after this test include bleeding or loss of amniotic fluid, which usually resolves on its own. There is a small risk of pregnancy loss with amniocentesis.
  • Chorionic villus sampling (CVS): Chorionic villus sampling involves taking a sample of the placenta (a biopsy) for testing. Tissue removal can be done either through the cervix (transcervical) or through the abdomen (transabdominal). This test is performed earlier in pregnancy than amniocentesis – between 10 and 13 weeks gestation. As with amniocentesis, there is a risk of miscarriage with CVS. Other risks include bleeding, rupture of membranes or infections.

Although most results can be “normal” or negative, this does not always mean that the baby has no chance of having a genetic condition.

Again, any result you get from a screening test is not a black and white or “yes”/”no” answer as to whether or not your child will have a certain disease or birth defect. Instead, screenings reveal the potential for certain conditions and birth defects. Positive screening tests are confirmed (or can be confirmed) by further testing.

A positive diagnostic test result means your baby is at a higher risk of having the genetic problem or birth defect the test was looking for. If this happens, your doctor will discuss the different options available and any additional care you may need during and after your pregnancy. Your doctor may also refer you to a specialist for more information about the specific disorder.

Can you refuse a genetic test during pregnancy?

Genetic testing is optional.

Whether or not you want to undergo genetic testing during your pregnancy is up to you. Talk to your doctor about the benefits versus the risks of testing. Your doctor can help you make an informed decision that is best for you and your baby. That said, your doctor cannot perform genetic testing without your consent.

Can you tell the sex of your baby through genetic testing?

Yes. You may be able to tell the sex of your baby through genetic testing. For example, the NIPT can be 98% accurate in predicting your baby’s gender. If the test detects a Y chromosome, your baby may be a boy. If the test does not detect a Y chromosome, your baby may be a girl.

How long does it take to get genetic test results?

The time it takes to receive your screening or test results will depend on the test, the type of technology used and the laboratory. In some cases, such as with FISH, you may receive your results in just a few days. Other methods, such as karyotyping, can take 1-2 weeks.

Are genetic tests covered by health insurance?

Some genetic tests may be included in your health insurance. Your coverage will depend on your policy and, in some cases, your risk factors, such as being over 35, a history of genetic problems, or other reasons for testing deemed necessary by your doctor. You can contact your health insurance fund for details.

If you have questions or concerns about genetic testing, make an appointment with your doctor.

The test is not mandatory, but you can discuss the recommendations during a preconception appointment or during your first prenatal visit.

Most women will test negative with both genetic screening and diagnostic tests.

For women who receive positive results, this information may be helpful in choosing further tests, receiving additional medical care, evaluating pregnancy options, or finding resources/support after the baby is born.

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