New Practice Guidelines for Prenatal Genetic Testing

Important guidelines in the area of prenatal genetics were recently published in the journal, Obstetrics and Gynecology (aka “The Green Journal”).  The American College of Obstetricians and Gynecologists (ACOG) and the Society of Maternal-Fetal Medicine (SMFM) collaborated on two new important references:  Practice Bulletin #162 Prenatal Diagnostic Testing for Genetic Disorders, and Practice Bulletin #163 Screening for Fetal Aneuploidy.  These are the first updated guidelines on these topics in nearly a decade and each offers a thorough assessment on currently available prenatal testing technologies as well important points to consider for any provider who provides prenatal care.  They are companion pieces and we encourage you to read them in their entirety when you have an opportunity. Below we summarize the highlights.  
Practice Bulletin number 162:  Prenatal Diagnostic Testing for Genetic Disorders

In 2007 ACOG shook things up by stating that all women (not just those deemed to have a higher chance to have a baby with a genetic condition) should have the option to undergo prenatal diagnostic genetic testing.  This recommendation did not change with the updated guidelines.  ACOG/SMFM still contend that all women should have the option of prenatal testing, including diagnostic tests such as amniocentesis and chorionic villus sampling (CVS). What has changed are the number of prenatal testing options.  With a growing number of testing choices, the decisions faced by expectant patients and couples are more complex than ever before. From the guideline:  

 

It is important that patients understand the benefits and limitations of all prenatal screening and diagnostic testing, including the conditions for which tests are available and the conditions that will not be detected by testing.”  

 

This is a great expectation!  Certainly even providers who think about these tests day in and day out struggle in deciphering the different benefits and limitations of each of these tests, as well as the variable conditions that each test may detect!  While it is perhaps a lofty goal, Genetic Support Foundation agrees wholeheartedly with the importance of this statement above. It is essential that individuals be provided enough information and context to make informed decisions when it comes to prenatal genetic testing.

Key updates with guideline #162:

  • Chromosomal microarray analysis should be the primary offered diagnostic method when ultrasound indicates structural abnormalities in the fetus.  Microarray should be made available to any patient choosing to undergo invasive diagnostic testing.  
  • New research indicates that the risk for miscarriage associated with amniocentesis and chorionic villus sampling may be lower than previously reported.  In the hands of experienced providers, the guideline suggests a miscarriage risk of 0.1% – 0.3%.  

Practice Bulletin number 163:  Screening for Fetal Aneuploidy

This document provides an excellent overview and nice comparison table of the various prenatal screening tests available for the assessment of chromosome conditions in the fetus. Technologies reviewed in detail include serum screening such as the triple and quad screening, combined screening such as first trimester screening, integrated screening and sequential screening and the more recently available cell-free DNA screening. The most important take away is that choices about prenatal screening options are complex.  

 

No one screening test is superior to other screening tests in all test characteristics. Each test has relative advantages and disadvantages. Screening for aneuploidy should be an informed patient choice, with an underlying foundation of shared decision making that fits the patient’s clinical circumstances, values, interests, and goals.”  

 

Key points with guideline #163:

  • Women who have any negative screening test should not be offered subsequent screening tests. Parallel testing with multiple screening tests should not be done.
  • Cell-free DNA screening is not a replacement for diagnostic testing.  
  • Any woman with a positive screening test including traditional serum screening or cell-free DNA screening results should be offered follow-up genetic counseling and the option to undergo diagnostic testing.
  • Women who undergo preimplantation genetic diagnosis should be offered aneuploidy screening and diagnostic testing.
  • Cell-free DNA screening for microdeletions is not recommended.  
  • Cell-free DNA screening is not recommended for multiple pregnancies.  

In the future, we will explore some points raised in these two guidelines in more detail including, the potential for toxic knowledge with chromosomal microarray testing and why genetic counseling in these situations. We will also explore the potential issues with predicting a lower risk of miscarriage associated with diagnostic testing at a time when some studies suggest that the risk may actually increase as fewer women undergo these tests and providers become less practiced in performing the procedures.  

One point that we strongly agree with is this:  

“Screening for aneuploidy should be an informed patient choice, with an underlying foundation of shared decision making that fits the patient’s clinical circumstances, values, interests, and goals.”  

Whether you are are patient, a healthcare professional, or policy maker, we at the Genetic Support Foundation hope that you will find information here on our website that will help support this goal.

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