ACOG - recommendations of the American Congress of Obstetricians and Gynaecologists regarding screening for Down syndrome

New Guidelines Recommend Universal Prenatal Screening for Down Syndrome

The American Congress of Obstetricians and Gynaecologists released the following guidelines regarding screening for Down syndrome.

Specific guideline recommendations based on good and consistent scientific evidence (level A) are as follows:

• First-trimester screening using both nuchal translucency measurement and biochemical markers is an effective screening test for Down syndrome in the general population. This screening strategy results in a higher detection rate than does the second-trimester maternal serum triple screen and a comparable rate to the quadruple screen, with the same false-positive rates.
• For first-trimester screening, measurement of nuchal translucency alone is less effective than is the combined use of nuchal translucency measurement and biochemical markers.
• Women found to have increased risk for aneuploidy based on first-trimester screening should be offered genetic counseling and the option of chorionic villus sampling or second-trimester amniocentesis.
• Nuchal translucency measurement for Down syndrome risk assessment should be limited to centers and individuals meeting the criteria for specific training, standardization, use of appropriate ultrasound equipment, and ongoing quality assessment.
• Women who elect only first-trimester screening for aneuploidy should be offered open neural tube defect screening in the second trimester.

Based on the type of testing women undergo they should be always fully informed on its detection rate, false-positive rate, advantages, disadvantages, limitations and risks. Women can refuse screening for many reasons. A woman's choice of a screening test is influenced by gestational age at her first prenatal visit, number of fetuses, previous anamnesis, availability of various methods, risk of invasice diagnostic procedures etc.

The following recommendations are based on limited or inconsistent scientific evidence (Level B):

• Screening and invasive diagnostic testing for aneuploidy should be available to all women who present for prenatal care before 20 weeks of gestation regardless of maternal age. Women should be counseled regarding the differences between screening and invasive diagnostic testing.
• Integrated first- and second-trimester screening is more sensitive with lower false-positive rates than first-trimester screening alone.
• Serum integrated screening is a useful option in pregnancies where nuchal translucency measurement is not available or cannot be obtained.
• An abnormal finding on second-trimester ultrasound examination identifying a major congenital anomaly significantly increases the risk of aneuploidy and warrants further counseling and the offer of a diagnostic procedure.
• Patients who have a fetal nuchal translucency measurement of 3.5 mm or higher in the first trimester, despite a negative aneuploidy screen, or normal fetal chromosomes, should be offered a targeted ultrasound examination, fetal echocardiogram, or both.
• Down syndrome risk assessment in multiple gestation using first- or second-trimester serum analytes is less accurate than in singleton pregnancies.
• First-trimester nuchal translucency screening for Down syndrome is feasible in twin or triplet gestation but has lower sensitivity than first-trimester screening in singleton pregnancies.

The following recommendations are based primarily on consensus and expert opinion (Level C):

• After first-trimester screening, subsequent second-trimester Down syndrome screening is not indicated unless it is being performed as a component of the integrated test, stepwise sequential, or contingent sequential test.
• Subtle second-trimester ultrasonographic markers should be interpreted in the context of a patient's age, history, and serum screening results.

References:

American College of Obstetricians and Gynecologists (ACOG). Screening for fetal chromosomal abnormalities. Washington (DC): American College of Obstetricians and Gynecologists (ACOG); 2007 Jan. 11 p. (ACOG practice bulletin; no. 77). 10 November 2010.

http://www.guideline.gov/content.aspx?id=10921