Prenatal DNA Testing: Top 6 Frequently Asked Questions

Before we get into the top questions that are asked in regard to prenatal DNA testing, let’s first get a bit into what the testing is about. The word prenatal literally means “before birth; during or relating to pregnancy.” In other words, prenatal DNA testing refers to testing that takes place at any of those times. Overall, a “prenatal test”covers screening or diagnostic tests from a given sample that is very informative to future parents. They can reveal potential health problemsthat could affect pregnant women and/or their unborn fetus, such as an increased risk of miscarriage or there are potential genetic disorders. For some of these conditions, there are treatments that can help, which is why these tests can be crucial.

A prenatal DNA test is based on the DNA that is extracted from the mother’s blood during the first, second and third trimesters. It is often referred to as NIPT that stands for non-invasive prenatal testing. The reason that these tests are based on the mother’s blood is because it contains bits and pieces of the baby’s DNA. This means that these tests are incredibly accurate in their screening of potential problems.

These potential problems the tests screen to look for the most common chromosomal abnormalities. These are

  • Trisomy 21 (Down syndrome), trisomy 18 and trisomy 13
  • 2 microdeletion
  • Monosomy X
  • Sex chromosome aneuploidies (SCA)

The procedure is simple. Mothers have their blood drawn at 10 weeks. This blood is sent to a laboratory for screening and analysis, after which the results are shared with the pregnant mother’s physician for discussion.

So, let’s get into some of the most frequent questions regarding this test.

1. How accurate are prenatal DNA tests?

Any test that is based on DNA technology is incredibly accurate. As such, prenatal DNA tests have successfully identified more than 99 percent of pregnancies with down syndrome. This is much higher than the success rates of traditional blood tests that have been known to miss as many as 15 percent of pregnancies with down syndrome.

Furthermore, these tests have a much smaller chance of yielding false-positive results. This type of result means that the test wrongly comes up as positive. By virtue of having fewer false-positives, this also saves time, money, and energy as physicians are much less likely to order follow-ups.

2. Can the test evaluate the baby’s gender?

Can the test evaluate the baby’s gender

Yes, the test can tell if the baby will be a female or a male. This is because the test is based on the baby’s DNA that is floating in the mother’s blood and which contains information pertaining to the baby’s gender. The nifty part about this is that mothers who have the test done find out about their baby’s gender at as early as 10 weeks, which is much earlier than what can be seen via an ultrasound.

3. Should pregnant women under the age of 35 take the test?

While studies have indicated that children of women who have given birth after the age of 35 are much more likely to suffer from a chromosomal abnormality, that is not the only indicator that the baby will have the disorders. Women who have given birth to a child with chromosomal abnormalities under the age of 35 and who would like to have another baby (still under the age of 35) are advised to have the test done as well. However, the tests are available to any woman who would like to know whether her baby is at risk of having a disorder, regardless of her age.

4. What are chromosomal abnormalities?

There are several, as mentioned above. A trisomy is a disease marked by an extra chromosome. Trisomy 21, termed as down syndrome, is marked by an extra copy of chromosome 21, while trisomy 18 and 13 are marked by extra chromosomal material of those two chromosomes.

Furthermore, a monosomy is a form of abnormality that is marked by the presence of just a part of the chromosome. Monosomy X means that one half of the X chromosome is missing.

Also, 22q11.2 microdeletion refers to missing genetic material on chromosome 22. Lastly, sex chromosome aneuploidies refer to a group of chromosome disorders that are marked by either missing or surplus genetic material on sex chromosomes.

5. If the test comes back positive, does that mean that my baby will have the disorder?

A prenatal DNA test is incredibly informative in regard to the health of the mother as well as the baby. However, great care should be taken while interpreting these results. While the tests are highly accurate, their results are not a diagnosis. In other words, just because a test came back as positive, this is by no means 100% certain that the baby will have a chromosomal abnormality. This just means that the baby has a high chance of having it based on the information in its DNA. As such, the prenatal DNA test ought to be viewed as a screening method rather than one that will provide a sure diagnosis.

6. How long does it take to receive results?

It does not take that long. Typically, a few days to a week go by between the day the blood is drawn to a doctor receiving the results. A small amount of blood is drawn from the pregnant woman, which is sent to an external laboratory for analysis. Once the laboratory assesses the blood, it sends the results to the physician’s office for a discussion with the patient.

Even though it was mentioned above, it is incredibly important to treat the DNA test results as an indicator rather than a diagnosis. These tests are screens and, as such, provide information as it pertains to risk. As such, great care ought to be taken with the analysis of the results.

Laura Day