To evaluate the role of 2nd trimester genetic sonography in a population that has already undergone 1st trimester Combined screening and 2nd trimester Quad screening.
Unselected singleton pregnancies at 15 centers had 1st trimester Combined screening at 10-13 wks (nuchal translucency, PAPP-A, fbhCG), and 2nd trimester Quad screening at 15-18 wks (AFP, hCG, uE3, inhibin-A). Patients remaining at their local FASTER site for antenatal care also had a detailed genetic sonogram at 15 to 23 wks, to evaluate for major structural fetal anomalies and minor markers for aneuploidy.
8,533 patients had detailed 2nd trimester genetic sonography, including 62 cases of Trisomy-21. 1st trimester combined screen detected 84% (52/62) of T-21 (6.6% FPR); 2nd trimester Quad screen detected 88% (53/60) (11% FPR). In the 3 T-21 cases undetected by these screens, multiple markers were detected in 2 and a major cardiac defect in 1, so that no T-21 were missed by the overall screening program. Use of likelihood ratios (LR) from the genetic sonogram to modify the risk of screening tests, resulted in higher detection rates for both 1st and 2nd trimester screens (92% and 93% respectively), and reduced the FPRs to 5.6% and 7.4% respectively.
The use of likelihood ratios from 2nd trimester genetic sonography improves the performance of 1st and 2nd trimester screens, by significantly reducing the FPR with further increases in detection rates.
© 2004 Elsevier Inc. Published by Elsevier Inc. All rights reserved.