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Rare Diseases

Prenatal Genetic Tests Offer New Noninvasive Options

Susan Klugman, MD, FACMG, FACOG

Board Director of Clinical Genetics, American College of Medical Genetics and Genomics

Genetic screening can occur as early as the embryonic stage as well as throughout a pregnancy. Carrier screening for genetic conditions like cystic fibrosis have become part of routine prenatal care. Patients determined to be a carrier of a genetic condition generally have no signs or symptoms, but their children are at greater risk.

Patients now have access to screening tests to determine if they are a carrier for hundreds of genetic conditions, as well as testing for abnormal chromosomal number in a fetus.

New ways to stay informed

NIPS (noninvasive prenatal screening) is the newest and most sensitive approach to Down syndrome screening. It relies on fetal DNA fragments in the mother’s blood that are shed from the placenta.

Using NIPS can result in false positives (i.e. a positive screening result that does not mean a fetus is affected). NIPS offers the lowest false positive rate when compared to other screening methods. All positive screening test results should be confirmed using amniocentesis or chorionic villus sampling (CVS).

A closer look at health

If a patient desires more information, diagnostic testing via amniocentesis or CVS should be considered. Amniocentesis is generally performed at 16-20 weeks of pregnancy, while CVS is done at 11-13 weeks. For each procedure, a sample is sent to the laboratory for chromosome analysis. An additional test called a microarray, where smaller parts of chromosomes/DNA segments are analyzed, can also be performed to help detect hundreds of other genetic disorders.

It is always the patient’s decision whether or not to opt for diagnostic testing, screening, or no screening/testing at all. 

Decisions on prenatal genetic screening and testing options can be complex. Healthcare providers can use guidelines and educational materials from national organizations like the American College of Medical Genetics and Genomics to help explain these concepts. Medical genetics professionals, such as genetic counselors and board-certified medical geneticists, are available to help interpret what the tests can and cannot tell.  

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