Definition
- Integrated screening combines first-semester and second-trimester screening to give one result after the second-trimester screen is completed.
- Sequential screening gives the risk after the first trimester if risk is higher than a specific cutoff and gives the combined risk after the second trimester if first-trimester risk was not higher than the cutoff. It can be further divided into stepwise and contingent.
- Stepwise screening: Women with risk above a certain cutoff following the first-trimester screen are offered invasive diagnostic testing directly, whereas women below cutoff are offered second-trimester screening.
- Contingent screening: Women with high risk are offered diagnostic testing, women with intermediate risk are offered second-trimester screening, and women with low risk have no further testing.
- Some centers prefer to divide patients into two groups only: Those with high risk who will be offered invasive testing directing and those who will proceed to second-trimester testing.
Use
- Risk assessment for trisomy 18, trisomy 21, and neural tube defects.
- 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
1American College of Obstetrics and Gynecology. Practice Bulletin, Clinical Management Guidelines for Obstetrician-Gynecologists #77, Screening for Fetal Chromosomal Abnormalities. 2007;109:217 " 227. 2Driscoll DA, Gross S. Prenatal screening for aneuploidy. N Engl J Med. 2009;360:2556 " 2562.