Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1153 page)

   Ultrasound in the first-trimester screen also contributes to detection of other chromosome abnormalities.

   Interpretation

   Approximately 95% detection of trisomy 21 with 5% screen-positive rate

   Limitations

   Noncompliant patients may not return for the second-semester screen.

Suggested Readings

American College of Obstetrics and Gynecology. Practice Bulletin, Clinical Management Guidelines for Obstetrician-Gynecologists #77, Screening for Fetal Chromosomal Abnormalities. 2007;109:217–227.

Driscoll DA, Gross S. Prenatal screening for aneuploidy.
N Engl J Med.
2009;360:2556–2562.

   
PRENATAL DIAGNOSTIC SCREENING

   Definition

   Noninvasive testing with goal of limiting invasive diagnostic procedures that carry risk to pregnancy.

   Use

   Screening modalities have been developed for Down syndrome/trisomy 21 detection because trisomy 21 is the most common viable autosomal chromosome abnormality. However, screening also provides specific risk assessment for trisomy 18 and neural tube defects.

   In addition, with inclusion of early ultrasound examination, increased fetal nuchal translucency may indicate other chromosome abnormalities including Turner syndrome (45,X), trisomy 13, and triploidy.

   Second-trimester measurement of AFP is used to assess risk of fetal neural tube defects.

   Screening is offered to all women, regardless of age, to provide more accurate risk information than provided by age alone.