Clinical article: screening for trisomy 13 using traditional combined screening versus an ultrasound-based protocol.

AIMS: To compare the screening capability of ultrasonography in detecting trisomy 13 (T13) using a multiparameter sonographic protocol (NT+) with a classical combined screening test (CST) protocol.

METHODS

The project was a prospective, multicenter study based on a nonselected mixed-risk population of women referred for a first-trimester screening examination. Each subject was offered a choice between either the gold standard, traditional combined screening test (CSG arm) or the ultrasound-based screening protocol (USG arm). General and MA-based screening performances were checked.

RESULTS

The study population comprised 20,887 pregnancies: 12,933 in the CSG arm, including 27 cases of T13, and 7954 in the USG arm, including 30 cases of T13. The DR for T13 was higher in the CSG arm than in the USG arm for all tested cutoff points: 1/50 (88.5 versus 63.3%, respectively), 1/100 (88.5 versus 70%, respectively) and 1/300 (92.3 versus 83.3%, respectively). Using the ROC curves for fixed FPRs of 3 and 5%, the T13 detection rate in our study reached 90 and 93%, respectively, in the USG arm and 92 and 96%, respectively, in the CSG arm. MA influenced the T13 screening performance in the USG arm and reduced the DR in patients <31 years. Such influence was not detected in the CSG arm.

CONCLUSIONS

Classic CST was more effective in detecting T13 than the ultrasound-only approach. However, the recommended cutoff of 1/50 showed unsatisfactory results for both traditional CST and the multiparameter sonographic test we proposed.