Several recent studies have shown that the addition of secondary ultrasound markers to the combined first-trimester screening for aneuploidies, or chromosomal abnormalities such as trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome), can slightly improve screening accuracy.
Traditional combined first-trimester screening, which is usually done between 11 and 14 weeks of gestation, uses the following measurements: maternal age, fetal nuchal translucency (NT) thickness, and blood levels of maternal serum free beta-human chorionic gonadotropin and pregnancy-associated plasma protein A. In a new study, researchers evaluated whether the addition of secondary ultrasound markers—assessment of the nasal bone, blood flow in the ductus venosus, and tricuspid regurgitation—to traditional combined screening could improve the effectiveness of first-trimester screening. Researchers found that using these secondary markers increased the rate of detection of aneuploidies from 87% to 92% and decreased the rate of false-positive results from 5.3% to 4.8%.1
In another study, when nasal bone, tricuspid regurgitation, and ductus venosus flow were used in conjunction with the traditional screening test (biochemical markers and NT), the detection rate for trisomy 21 increased from 93.8% to 100% and the rate of false-positive test results decreased from 4.84% to 3.4%.2 The timing of these tests may also be important. According to a literature review, first-trimester screening could be improved by conducting the biochemical test between 9 and 10 weeks of gestations and performing the ultrasound examination—using the secondary screening parameters of assessment of the nasal bone and blood flow in the ductus venosus, hepatic artery, and across the tricuspid valve—at 12 weeks.3
These findings have clinical significance because a decrease in the number of false-positive test results would subsequently lower the number of unnecessary invasive diagnostic tests and reduce the risk of possible complications that are related to certain tests, such as miscarriage or cramping and vaginal bleeding with amniocentesis.
Pertinent Points:
- While risk of assessment using combined biochemical markers and nuchal translucency measurement has an acceptable screening performance, it can be improved by integrating secondary ultrasound markers into the first-trimester screening evaluation.
