Breakthroughs | Pregnancy
November 3, 2016

Advances in genetic testing for pregnant women

by pregnancy

New screening gives pregnant women a less-invasive route for prenatal genetic testing.

 

In the last five years, genetic testing technology has improved dramatically. Medical professionals are now able to predict more about a baby before it is born then was ever possible before.

One of the most exciting advances has been the ability to analyze a pregnant patient’s blood for a few common genetic conditions, such as Down syndrome. This screening test can reduce the need for an invasive procedure such as amniocentesis or chorionic villus sampling, both of which carry a slight risk of miscarriage.

This new test is called non-invasive prenatal screening and is also known as cell-free DNA screening. The screening analyzes small fragments of genetic information from the placenta that can be detected in the maternal blood stream during pregnancy.

This screening measures quantities of fragmented DNA to estimate the risk for a few common chromosome abnormalities. Because this technique is a screening test, it cannot confirm or rule out a chromosome abnormality. However, results reported as “low risk” indicate a 99 percent chance that a pregnancy is not affected with common chromosomal disorders such as trisomy 21 (Down syndrome), trisomy 13 and trisomy 18, as well as a number of sex chromosome abnormalities such as Turner syndrome and Klinefelter syndrome.

If a non-invasive prenatal screening result is reported as “high risk,” the patient is asked to confirm this result via a diagnostic test either during the pregnancy or after the birth of the baby. During the pregnancy, an amniocentesis or chorionic villus sampling can determine the accuracy of the high-risk results. These tests are more comprehensive than the non-invasive prenatal screen and will allow for the diagnosis of a chromosome condition, in addition to other genetic abnormalities including microdeletions, microduplications and single gene disorders.

Non-invasive prenatal screening does not screen for all genetic conditions or birth defects, so patients with a specific family-history concern or those who desire more genetic information about a pregnancy should meet with a reproductive genetic counselor.

Vanderbilt has three reproductive genetic counselors who counsel all patients who want non-invasive prenatal screening or more information about their reproductive risks and screening options.

This post was written by Vanderbilt University Medical Center’s Martha Dudek, MS LCGC, Jill Slamon, MAT, MS LCGC, Caitlin Grabarits, MGC, LCGC, and Frank H. Boehm M.D.

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