Prenatal Genetic Testing, Explained

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Image via Flickr/Andrewmalone

For many women, the appearance of that positive pregnancy test brings a mixture of excitement and trepidation.

Because the experience of pregnancy, while a joyous and miraculous one, also carries it with an-ever present and haunting question of, what if something goes wrong?

Could there be something wrong with my baby?

Some parents might choose to consider genetic testing during their pregnancies for a peace of mind or planning for the future, while other couples (myself included) aren’t really sure what genetic testing during pregnancy even involves.

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Image via Flickr/Andrewmalone

Explaining genetic testing during pregnancy

Basic genetic testing uses a combination of ultrasound and blood samples from the mother to screen for genetic disorders, such as Down’s syndrome. Usually, the tests are considered preliminary and if they come back positive, will require a more invasive amniocentesis (a test that takes a sample of amniotic fluid using a needle) for confirmation. Couples with abnormal results will also be offered genetic counseling to discuss their options for the future. 

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First Trimester Tests

According to Lucile Packard Children’s Hospital in Stanford, first trimester testing for genetic disorders involves two main tests. The first is a fetal nuchal translucency (NT), which uses a regular ultrasound to measure the fluid at the base of the baby’s brain, while the second looks at hormones and proteins produced by the placenta through a blood sample by the mother. Taken together, any abnormalities in the tests can point to birth defects, such as Down syndrome, trisomy 18, or trisomy 13.

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Second Trimester Tests

During the second trimester, things can get a little more intense on the testing scale. Doctors generally consider it more helpful for accurate results if a woman receives first trimester testing before moving on to the second trimester tests, so if you are interesting in genetic testing, be sure to speak to your provider early on in the pregnancy.

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Multiple-Marker Screening

For second trimester testing, another blood sample from mom is taken between 15-20 weeks of pregnancy and tested for what are called “multiple markers,” which is just a fancy way of saying they use a bunch of different tests together to look for abnormalities. The tests look at hormones produced by the placenta as well as the level of alpha-fetoprotein in the mother’s blood. Alpha-fetoprotein is a protein produced by the baby’s liver; abnormal levels can indicate spina bifida, Down syndrome, and other defects.

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Considerations

It’s extremely important to understand that genetic testing is not meant to serve as a guaranteed indicator if your baby has a birth defect, but is meant to be a screening tool for additional testing. Preliminary prenatal genetic testing is not 100% accurate; there are cases of false positives or even false negatives, so you will need to weigh the pros and cons of having any type of genetic testing done during your pregnancy. If you are older than age 35, have a history of any genetic disorders in the family, or were exposed to any potentially hazardous substances during your pregnancy, you may want to consider testing.

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What happens if your test comes back positive?

As I explained, health experts stress that genetic testing cannot be considered 100% accurate; the prenatal screening tools are simply that – screening tools – and can’t offer parents a definitive diagnosis. Further testing, usually in the form of more ultrasounds and an amniocentesis, might be needed. You will also be offered genetic counseling to sit down with a professional who can help guide you in the next steps.

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Common Birth Defects

Dr. Genevieve Fairbrother, M.D., M.P.H. explains that “genetic disorders may be inherited from parents who pass on affected genes or they may occur randomly. According to Dr. Fairbrother, genetic testing can screen for both types of conditions and couples from certain ethnic backgrounds or those with a family history of a disorder may benefit from genetic screening prior to pregnancy. Such conditions include Sickle Cell Trait, Cystic Fibrosis, Spinal Muscular Dystrophy, Hemophilia, Huntingdon's disease, or any of the conditions in the Ashkenazi Jewish panel. There are different types of testing methods for these conditions, and those can be performed during a pregnancy to help identify Down syndrome (trisomy 21), Trisomy 18 and Trisomy 13 as well as X and Y sex chromosome conditions. One advanced and recently introduced method is non-invasive prenatal testing (NIPT), which includes tests such as the Harmony™ Prenatal Test. “NIPTs can be performed as early  as 10+ weeks gestation and are a more accurate way for assessing the risk for trisomies and sex chromosome aneuploidy,” says Dr. Fairbrother.

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What’s the treatment?

Some genetic disorders that can be detected while you are still pregnant, like structural abnormalities, are treatable, while others are not. Again, there is no guarantee when undergoing testing and your health care provider can help you walk through the steps if any abnormality is suspected.

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{Related:  Fetal Genetic Testing}

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What do you think?

Prenatal Genetic Testing, Explained

Chaunie Brusie is a writer, mom of four, and founder of The Stay Strong Mom, a community + gift box service for moms after loss. ... More

Tell us what you think!

4 comments

  1. Sara says:

    My opinion is that, its better to do the genetic testing before conceiving. Genetic testing done during the pregnancy period is little more complicated. Its always better to take precaution as soon as possible than crying over the results later. I’m living in Dubai and i got my genetic test done here in FML Dubai before conceiving. By gods grace, the result was negative.

  2. Nicole says:

    You’re right Chaunie, you don’t know much about it! The QUAD screen (that u describe in detail) is old practice!!! You should be writing an article about fetal DNA (Maternity21 and The Harmony) blood testing!!!! If you research the stats on the QUAD vs. the fetal DNA it is not a comparison! Fetal DNA is 99.7% accurate where as the QUAD is only ~80% with a false positive of about 20%!!!

    • Hi Nicole, thank you for your comment. I did describe the quad screen for a type of testing that is available during the second trimester, but not as an all-inclusive type of testing that is available. And if you click through the rest of the slides, I did include information on the Harmony test as well. I was able to speak with a representative from the makers of the Harmony testing, so that was very useful information. Thanks again for reading and pointing out the statistics!

  3. angel says:

    I had the genetic testing done during my first trimester and second trimester. Where I went they were very good. I was a high risk pregnancy due to my age and we went thru IVF. We knew the risks as it was explained to us. The first screening the doctor said something could be wrong with our baby and gave us options we could do and we said no. it didn’t make a difference if their was a problem with our baby. we would love our baby no matter what. The second test they did they found nothing wrong with our baby except that he didn’t want to cooperate with the ultrasound tech when they were doing the test.. I’m grateful they offered the testing to us. The only test I refused was the ammio and glucose

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