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New Screening Guidelines for Fetal Chromosomal Abnormalities

Screening options for Down syndrome include combinations of serum markers and ultrasonography.

The development of several markers and strategies for prenatal detection of Down syndrome has prompted the American College of Obstetricians and Gynecologists to update its practice guidelines for screening for fetal chromosomal abnormalities. Counseling all pregnant women, regardless of age, about the availability of screening tests for fetal aneuploidy is now recommended. Several screening schema have been evaluated; many include the combination of biochemical markers (e.g., serum pregnancy-associated plasma protein [PAPP-A] and free or total ß-human chorionic gonadotropin [ß-hCG]) and ultrasound-guided measures of nuchal translucency. In light of these options, the detection rate for Down syndrome varies from 70% to 95%, with a 5% false-positive rate. Highlights of the guidelines include the following recommendations based on good and consistent scientific evidence (Level A):

• First-trimester screening with biochemical markers and nuchal translucency measurement is effective for detecting Down syndrome in the general population; measurement of nuchal translucency alone is less effective.
  
• If first-trimester screening reveals an increased risk for aneuploidy, genetic counseling and chorionic villus sampling (CVS) or second-trimester amniocentesis should be offered.
  
• Optimal nuchal translucency measurement requires experience, standardization, and appropriate ultrasound equipment and should be performed only in facilities that meet these criteria.
  
• Second-trimester screening for neural tube defects should still be offered to women who have had first-trimester testing for aneuploidy.
  

Comment: Screening with serum biomarkers and ultrasound has the advantage of being low risk, but this approach will not detect all cases of aneuploidy. Diagnostic testing — CVS or amniocentesis — is more reliable but does carry a small risk for pregnancy loss (Journal Watch Women’s Health Nov 9 2006 and Jan 11 2007). Decisions about which tests to offer should be guided by local availability, trimester of pregnancy, and patient preference. Women of any age should be offered the option of invasive testing because each woman weighs the various pros and cons differently. By adopting standardized screening algorithms that utilize resources available in their communities, clinicians can help their patients make informed decisions based on individualized risk assessment.

— Anna Wald, MD, MPH

Published in Journal Watch Women's Health March 8, 2007

Citation(s):

ACOG Committee on Practice Bulletins. ACOG Practice Bulletin No. 77: Screening for fetal chromosomal abnormalities. Obstet Gynecol 2007 Jan; 109:217-28.

• Medline abstract (Free)

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