Should the first-trimester aneuploidy screen be maternal age adjusted? Screening by absolute risk versus risk adjusted to maternal age.

OBJECTIVE To compare the absolute risk (AR) screening approach to the current approach of risk adjusted to maternal age in patients undergoing first-trimester screening (FTS). MATERIAL AND METHODS Three-stage retrospective analysis of 3073 pregnancies that had FTS during 2006-2007. (1) Distribution analysis of AR as defined by (final FTS risk)/(risk by age). (2) Analysis of the screen-positive group by the AR method. (3) Analysis of the screen-positive advanced maternal age (AMA) patients. RESULTS (1) AR > 1 was found in 151 (4.9%) patients, and AR > 1.2, 2 and 3 was found in 4, 3.1 and 2%, respectively. (2) 145 (4.7%) of the 3073 patients screened positive. Twelve were diagnosed with chromosomal abnormalities and 3 with major anomalies. All had AR > 1.2. Of the 145 (55.8%) screen positives, 81 had AR > 1.2. AR was significantly higher in the chromosomally abnormal as compared to normal gestations (t-test, p < 0.01). (3)Of the 145 screen positives, 103 were AMA. Only 39 (28%) had an AR > 1.2. CONCLUSIONS The AR screening approach, using AR > 1.2 as a cut-off, captured all abnormal pregnancies diagnosed by the current screening method. This method offers lower false positive (FP) rates to AMA women and has the potential for higher detection rates in younger women.