Sequential testing for Down syndrome: the impact on estimated risk

Our objective was to describe the utilization of sequential screening and evaluate the impact on estimated Down syndrome risk.

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.

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%.

Sequential testing lowers the Down syndrome risk in most cases and is more likely to do so with decreasing first-trimester risk.