Choice of follow-up testing after a positive first-trimester Down syndrome screening test (August 2018)
Pregnant women who screen positive for Down syndrome on the first-trimester combined test may choose to undergo secondary screening with a cell-free DNA test or proceed to an invasive test for definitive diagnosis. In a multicenter trial including over 2000 women comparing the two approaches, no Down syndrome pregnancies were missed, but two fetuses with microdeletions were detected in the invasive testing group that would not have been detected by cell free DNA testing. Although the number of invasive procedures performed was dramatically lower in the cell free DNA group, the miscarriage rate was similar for both groups. Major limitations of the trial were differences between groups in patient compliance with the study protocol and lack of statistical power to identify a very small difference in miscarriage rate. We continue to offer both options to women who screen positive for Down syndrome on the first-trimester combined test.
(from UpToDate)