3 Genetics Tests To Improve Prenatal Screening

07/26/2017 12:46 pm ET Updated Jul 26, 2017

This article is authored by the Mayo Clinic Center for Individualized Medicine. The mission of the Center is to discover and integrate the latest in genomic, molecular and clinical sciences into personalized care for patients.

New technology is reshaping prenatal screening to assess the health of a developing baby. Now pregnant women can have their baby initially screened for genetic disorders, such as Down syndrome, through the use of a newer blood test that evaluates DNA present in the mother’s blood stream. Another test for couples planning a family uses a single blood sample to assess whether future children might be at risk for developing a genetic disease.

“It’s an exciting time in perinatal testing,” explains Myra Wick, M.D., Ph.D. “DNA sequencing and molecular technology have improved and become more cost effective. These tests are important for family planning before pregnancy as well as planning for the care of a baby who is found to have a genetic disorder during pregnancy. ”

Researchers from Mayo Clinic and the Center for Individualized Medicine have helped implement several of these tests, which use a personalized medicine approach to perinatal screening. Three state-of-the-art perinatal genetic tests are becoming more widely available to expectant parents.

1. Cell free DNA testing

Mayo Medical Laboratories recently launched a blood test to screen for the most common chromosome disorders diagnosed in pregnancy, such as Down syndrome. It’s known as a cell-free DNA test. It screens the mother’s blood that contains DNA from the baby, looking for genetic disorders in the fetus. The new test generally has a higher detection rate and fewer false positives than traditional screening tests.

“Prior to this new test, mothers had the option of traditional first trimester screening, which is a blood test and ultrasound, or second trimester screening, which is a blood test. In general, the cell free DNA blood test can be used in place of the traditional first and second trimester screening,” explains Dr. Wick. It is important to remember that the cell free DNA testing is a screening test, and abnormal results should be followed up with additional testing.

The out-of-pocket cost for the new blood test varies depending on insurance coverage, and the specific laboratory performing the testing; a general estimate is approximately $350. Results are usually ready within one week.

2. Expanded carrier screening

In the past, couples had genetic screening based on family history of a genetic disorder, or if they were part of an ethnic group at risk for certain inherited diseases. Previous tests only screened for a small defined group of genetic disorders. Those tests didn’t help couples who were uncertain of their ethnic heritage, plus the tests were very limited in scope.

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“It’s an exciting time in perinatal testing. DNA sequencing and molecular technology has improved and become more cost effective. These tests are important for family planning prior to pregnancy as well as planning for the care of a child who is found to have a genetic disorder during pregnancy. ” - Dr. Myra Wick

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Now couples may choose a more comprehensive test that looks for 100 or more genetic disorders. It’s called expanded carrier screening. This test is done with a blood sample from each prospective parent.

“Expanded carrier screening looks at multiple genes associated with genetic diseases. Most of the disorders included on an expanded carrier screen are inherited in an autosomal recessive manner. This means that the parents are carriers of the disorder, with one normal copy of the gene and one abnormal copy of the gene. Carriers of an autosomal recessive disorder do not typically have signs or symptoms of the disease. A child is affected with an autosomal recessive disorder when he or she inherits one abnormal copy of the gene from mom, and one abnormal copy of the gene from dad. Approximately 5% of couples who undergo expanded carrier screening are found to be carriers for the same disorder, and at risk for having an affected says Dr. Wick.

Depending upon insurance coverage, the test costs approximately $350. Test results are returned within one to two weeks.

3. Whole exome sequencing (WES)

In rare cases, an ultrasound during pregnancy reveals that the baby has several medical problems. Traditional genetic testing may not identify a diagnosis. Now whole exome sequencing (WES), which looks at most of the genes linked to growth and health, can be used to evaluate the fetus’s condition. It can provide a diagnosis in 30 percent of cases.

For this testing, an amniocentesis is performed first to obtain DNA for genetic analysis.

“We are beginning to use WES even before the baby is born. Results can be used to plan for care of an infant who may be born with several complex medical concerns. In addition, parents can use this information for future family planning,” says Dr. Wick.

Whole exome sequencing is expensive, with typical costs of approximately $8,000, depending upon the specific test and insurance coverage. Results from this more complex screening usually take several weeks, depending upon the specific test being used.

Seek genetic counseling

Dr. Wick’s suggests that you ask your health care provider about genetic testing and recommends that all prospective and expectant parents consult with a medical geneticist or genetic counselor before genetic screening.

If your provider is at a large medical center, genetic counseling should be available. At smaller facilities, your primary provider may order initial blood tests, but you may be referred to a larger facility if test results indicate you need genetic counseling.

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