••• CHAPTER 65^ ACOG Screening Guidelines Since 2007^657
❍ What is the difference between the stepwise sequential screen, the contingent sequential screen, and the
integrated screen?
The stepwise sequential screen reports the results of the first-trimester analyte screen with NT and the combined
second-trimester analyte screen.
The contingent sequential screen reports the first part of the sequential and does not test low-risk patients in the
second trimester.
The integrated screen incorporates the first- and second-trimester analytes plus or minus the NT in one final report.
❍ Which tests should be offered?
If a patient presents in the first trimester, integrated testing should be offered and if they present in the second
trimester, a quad screen should be offered.
❍ When can an NT be performed?
Between 10.4 and 13.6 weeks.
❍ How many fetuses with an increased NT will have a chromosomal abnormality?
One-third.
❍ Why is first-trimester screening preferred?
If there is a positive screen before 14 weeks, CVS may be offered and early termination may be preformed if
desired.
❍ What should be offered to patients with increased risk of aneuploidy?
Genetic counseling and chorionic villous sampling or amniocentesis.
❍ What should be offered if a patient has an NT >3.5 cm?
The patient should be offered a targeted fetal ultrasound and fetal echocardiogram because heart defects,
abdominal wall defects, and genetic syndrome may be associated with this finding.
❍ What are other markers of aneuploidy in the first trimester?
Absent nasal bone, crown-rump length, femur and humeral length, head and trunk volumes, and umbilical cord
diameters.
❍ What are other markers of aneuploidy in the second trimester?
Echogenic bowel, cardiac echogenic focus, and dilated renal pelvis.
❍ How is aneuploidy screening affected in multiple gestations?
It is less accurate in both the first and the second trimester but can still be performed.