A graphical analysis of the results suggested that all analytes, except AFP, showed a material discrimination between affected and unaffected pregnancies.
The screening performance of CT ratios was significantly better with the first trimester measurements at 11 weeks than at 12 or 13 weeks.
The performances of the conventional and new versions of integrated screening were expressed as the DR for a specific FPR and the FPR for a specific DR. For example, at a 90% DR, the integrated test (in which total hCG was used) yielded an FPR of 0.67% with CT ratios and 2.15% without CT ratios, a proportional reduction of 68%. The corresponding estimates for the serum integrated test (at a 90% DR) were 2.37% and 8.12%, respectively, a similar proportional reduction. A comparable reduction in FPR rate was also found when assuming an 85% and 95% DR.
The screening performances of the tests were influenced little by whether total or free beta-hCG was used. With the addition of CT ratios to the integrated test, and with first-trimester measurements performed at 12 rather than 11 completed weeks, the FPR for a 90% DR approximately doubled to 1.29%, and at 13 weeks it was 2.12%.
A cumulative analysis showed that most of the gain in screening performance came from CT ratios for PAPP-A and uE3.
Other important results were as follows:
the integrated test with CT ratios had the best screening performance;
the serum integrated test with CT ratios had similar screening performance to the integrated test without CT ratios; and
the serum integrated test without CT ratios had the poorest screening performance.
Screening performance was reduced by dropping any of the markers. The loss was greatest when PAPP-A was dropped and least with inhibin-A. For example, after excluding the measurement of inhibin-A, the integrated test with uE3, hCG and PAPP-A CT ratios gave an FPR of 1.02% for a 90% DR, compared with an FPR of 0.67% if inhibin-A were retained as a marker.
The best risk cut-off level was estimated to be 1 in 150 with either the integrated or serum integrated test, achieving detection rates of about 93% and 89%, respectively, and FPRs of about 1.3% and 2.2%.