Editorial: Getting NT screening ready for prime time

December 1, 2005

Regardless of the specific screening option chosen, what is clear is that the inclusion of NT measurements optimizes Down syndrome screening.

The aim of the "FASTER" (First and Second Trimester Evaluation of Risk) study was slightly different: to compare first- and second-trimester testing for Down syndrome.1 The first-trimester approach was the same as the BUN trial, but results were withheld from a patient until second-trimester serum analyte results were available-unless the NT measurement was extremely elevated and the fetus had a cystic hygroma. More than 38,000 women from around the country participated in FASTER. The study found that both first- and second-trimester screening could detect around 85% of fetuses with Down syndrome, but that the screen-positive rate to achieve this detection efficiency was one third lower with first-trimester screening (see Table). They also noted that combining first- and second-trimester testing could yield even better results. A stepwise integrated approach provides patients the results of the first-trimester screen so they have the option of a CVS. It then combines the results of first- and second-trimester screening to produce a final risk assessment. This approach detected 95% of Down syndrome fetuses, for an overall 4.9% screen-positive rate.

Thus, patients now have a menu of options for Down syndrome screening. The advantages of first-trimester screening were articulated in an editorial accompanying the FASTER publication by Contemporary OB/GYN's long-term Editorial Board member Dr. Joe Leigh Simpson.3 He pointed out that earlier detection of increased Down syndrome risk permitted CVS, which is quite safe in experienced hands, as well as earlier terminations for patients who chose to abort affected pregnancies. Such earlier terminations are more private and safer. Thus, use of either first-trimester screening alone or the stepwise integrated option may well be the optimal approach.