Sequential testing for Down syndrome: the impact on estimated risk.

Overview

OBJECTIVE: Our objective was to describe the utilization of sequential screening and evaluate the impact on estimated Down syndrome risk. METHODS: We reviewed records of all those undergoing first-trimester screening over a 3-year period. All patients received first-trimester Down syndrome risk, and had options of invasive testing and sequential testing. We compared adjusted first-trimester Down syndrome risk with adjusted risk following sequential testing. Fisher's exact test and chi-square for trend were used for statistical comparison. RESULTS: First-trimester screening was performed on 12,557 patients. The rate of sequential testing was 34.0%. In 13.1% of patients, sequential testing resulted in a higher risk compared with first-trimester risk, with a risk at least twice as high in 5.2%. The likelihood that sequential testing would increase risk progressively decreased as first-trimester risk declined, from 17.8% for those with first-trimester risk of >1 in 270 to 8.7% in those with first-trimester risk of <1 in 10,000 (p < .001). For those with first-trimester risk <1 in 2000, the likelihood that sequential testing would adjust risk to >1 in 270 was <1%. CONCLUSIONS: Sequential testing lowers the Down syndrome risk in most cases and is more likely to do so with decreasing first-trimester risk.