When most people think of DNA testing, they think of dramatic courtroom scenes from TV shows that reveal the perpetrator of a crime. We now also regularly hear stories of people using DNA testing to answer questions about their ancestry, sometimes discovering blood relatives they didn't know they had.
In the context of pregnancy, the role of DNA testing is to detect genetic diseases in a fetus. (An added bonus for parents is learning the sex of the baby, which many are eager to know.) Unfortunately, genetic testing during pregnancy is often not as conclusive or straightforward as the DNA tests that police use to determine whether someone is was at the scene of an assault. crime.
A recent study shows that more extensive testing can be done through a maternal blood test earlier in pregnancy than the tests we currently have access to. This means that expectant parents will soon be able to know much more about their baby's genome, potentially identifying many genetic diseases during the first trimester of pregnancy.
However, the results of these tests are not always clear and patients may need help understanding what they mean and whether they need to have additional tests.
What types of prenatal genetic tests are available now?
Currently, pregnant patients in the US are offered two types of tests: screening tests and diagnostic tests. Screening tests are generally offered toward the end of the first trimester. One screening test is the cell-free fetal DNA test (also called non-invasive prenatal testing or NIPT), which only requires a blood sample from the pregnant person. Another example is the nuchal translucency examination, which measures a fluid-filled space at the back of the fetus' neck, performed via ultrasound. These tests are used to screen for various chromosomal abnormalities, including Down syndrome or trisomy 21.
Because both tests are considered screening tests, they indicate how likely your baby is to have a condition, rather than a diagnosis. Depending on the results of those tests, you may be offered a diagnostic test to determine whether the fetus does indeed have a genetic condition. These tests, chorionic villus sampling (CVS) and amniocentesis, are offered slightly later in the pregnancy: CVS at 11 to 13 weeks and amniocentesis at 15 to 20 weeks. These tests examine DNA samples taken from the placenta (CVS) or the amniotic fluid surrounding the fetus (amniocentesis). Diagnostic tests can reveal a much wider range of chromosomal abnormalities by examining all genes of the fetus for microdeletions and duplications. Holly Mueller, a genetic counselor at the University of California, San Francisco, told HuffPost that such tests can screen for about 5,000 conditions.
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The advantage of the diagnostic tests is that the results are very accurate and can detect a large number of conditions. The disadvantages are that they occur later in pregnancy, which means that depending on your state's abortion restrictions, you may have to travel to another state if you decide to terminate the pregnancy. For example, in Florida, abortion is prohibited after the 15th week of pregnancy.
There is also a small risk of miscarriage with both procedures. Mueller said the risk of miscarriage with these tests is about 1 in 450 for CVS and 1 in 900 for amniocentesis.
What tests will be available in the future?
A small study involving 36 patients was published in November in the New England Journal of Medicine. Researchers took a blood sample from each patient, as you would do with a cell-free fetal DNA test, and then, using new technology known as 'deep trio-exome sequencing', they screened for a host of genetic disorders, as you would with the sample from an amniocentesis or a CVS test. This new test is called the desNIPT test.
"The purpose of the study is to see if we can do the same thing as with the invasive sample [CVS or amniocentesis] ... using a non-invasive test," meaning the blood sample, Martin Larsen, one of the study's authors, told HuffPost.
The results showed that using this new technology, the results of the desNIPT tests were as accurate as the results of an amniocentesis. Larsen, a clinical laboratory geneticist at Odense University Hospital in Denmark, said there were no false positives in any of the patients involved in the study. A number of genetic diagnoses were made, including heart disease and dwarfism. The blood test results were confirmed by CVS or amniocentesis in these patients (all of whom were considered high risk). That is, both tests - the blood test and the invasive test (CVS or amniocentesis) produced the same results.
If further studies replicate this level of accuracy, desNIPT testing could become the norm in the first trimester of pregnancy for many genetic conditions.
Pregnant people could get results earlier in the pregnancy, in the first trimester (the cell-free fetal DNA test is currently offered from 10 weeks) - and without the risk, however small, of one of the invasive tests.
Another important advantage would be the ability to test for so many types of genetic conditions so early in pregnancy. As it stands now, Larsen explains, patients are often referred for invasive tests after suspected abnormalities are seen on an ultrasound.
"There's a group of genetic diseases where you see deformities during pregnancy, and then there's a very large group of genetic conditions where there's no indication during pregnancy that there's a problem." In other words, there are many genetic conditions that do not show up on an ultrasound, meaning the patient is not referred for further testing.
"The potential is that this method could identify these pregnancies much earlier than what is happening now," Larsen said.
In the report, the authors estimate that it will take seven days for patients to receive test results.
What are possible concerns about this new test?
More results sooner sounds like a win-win situation. But there are a few areas of concern.
The first is one of access. "One obstacle is the pricing of the test," says Larsen. "It's quite expensive at the moment." The cell-free fetal DNA test is expensive, and the new desNIPT may be even more expensive. He hopes further innovation will reduce costs.
Mueller is concerned that in a country like the US, which does not guarantee healthcare, there could be wide disparities in who has access to the test. She said she already sees income disparities in who has access to genetic testing - with people with higher incomes more likely to get diagnostic tests - and a new, more expensive test could widen the disparities even further.
Mueller is also concerned about accuracy, as the recent study was small and there is potential for errors in the test results.
"I would feel really uncomfortable, at least at this point, if patients were making reproductive decisions based purely on the non-invasive results," Mueller said.
If a screening test was positive, she would still recommend that a patient have follow-up diagnostic testing to be more certain. Mueller noted that some patients in the United Kingdom make reproductive decisions based on a currently available non-invasive test, but this is now not common in the US.
Another major difference between Europe and the US is access to abortion care. Currently, 15 US states have near-total bans on abortion, meaning patients in those places need the financial resources to travel for a procedure. For example, in a recent case in Texas, a woman whose fetus was diagnosed with trisomy 18 (a fatal condition) sued the state for access to abortion and ultimately left the state to terminate her pregnancy.
For now, Mueller asks the following questions for patients considering genetic testing: "Are you okay with potentially getting a result that clouds rather than clarifies matters? And are you willing to take additional steps after we receive that result to potentially get more information, such as diagnostic testing?
"As long as you receive the right guidance, I think it is important that patients receive tests that they feel are important and relevant to them."