Contribution of 'modified genetic sonography' to the combined test as a screening method for chromosomal abnormalities

We propose to assess the contribution of "modified genetic sonography" (MGS) to the combined test (CT) as a method of stepwise sequential screening (1st step: CT, 2nd step: MGS) for chromosome abnormalities in the general population of pregnant women.Prospective study. During a 4 year study period (July 2005-June 2009) 16,548 pregnancies underwent a CT combined with MGS (major malformation and nuchal fold) as a screening method for chromosome abnormalities. We assessed sensitivity and false positive rate (FPR) (95% CI).We offered a chromosome abnormalities screening test to 96.6% of pregnancies (15,995 cases). 14,160 cases are analyzed (1st step: CT, 2nd step: MGS) including 49 chromosome abnormalities and 35 Down's syndrome (DS). The sensitivity of CT for DS was 77.1% [95% CI, 63.2-91] (27/35) and 77.5% for all chromosome abnormalities [95% CI, 65.8-89.2] (38/49) with a FPR of 4.4% [95% CI, 4.1-4.7]. If MGS was combined with CT, the sensitivity for DS was 91.4% [95% CI, 82.1-99] (32/35) and 93.8% for all chromosome abnormalities [95% CI, 87-99] (46/49) for a FPR of 5.1% [95% CI, 4.7-5.5].The addition of an MGS to combined first-trimester screening test for aneuploidy improved sensitivity by 14.3% while only increasing the FPR by 0.7%.