Retrospective study evaluating the performance of a first-trimester combined screening for trisomy 21 in an Italian unselected population.

OBJECTIVES: to assess the performance of a combined first-trimester screening for trisomy 21 in an unselected Italian population referred to a specialized private center for prenatal medicine.

METHODS: a retrospective validation of first-trimester screening algorithms [risk calculation based on maternal age and nuchal translucency (NT) alone, maternal age and serum parameters (free β-hCG and PAPP-A) alone and a combination of both] for fetal aneuploidies evaluated in an unselected Italian population at Artemisia Fetal-Maternal Medical Centre in Rome. All measurements were performed between 11(+0) and 13(+6) weeks of gestation, between April 2007 and December 2008.

RESULTS: of 3,610 single fetuses included in the study, we had a complete follow-up on 2,984. Fourteen of 17 cases of trisomy 21 were detected when a cut-off of 1:300 was applied [detection rate (DR) 82.4%, 95% confidence interval (CI) 64.2-100; false-positive rate (FPR) 4.7%, 95% CI 3.9-5.4; false-negative rate (FNR) 17.6%, 95% CI 0-35.8%].

CONCLUSION: in our study population the detection rate for trisomy 21, using the combined risk calculation based on maternal age, fetal NT, maternal PAPP-A and free β-hCG levels, was superior to the application of either parameter alone. The algorithm has been validated for first trimester screening in the Italian population.