The Society of Maternal-Fetal Medicine 24th Annual Clinical Meeting kicked off with the long-awaited results of the First and Second Trimester Evaluation of Risk (FASTER) Trial. There were several abstracts related to this study. The central presentation derived from this protocol confirmed the validity of previous studies that the use of a first-trimester ultrasound determination of the nuchal translucency combined with 2 serum markers is a viable alternative to the traditional second-trimester maternal serum screening for Down syndrome. This impressive protocol enrolled more than 33,500 women with singleton pregnancies between 10 3/7 and 13 6/7 weeks, at which time they underwent serum screening with pregnancy-associated plasma protein A (PAPP-A) and free beta-human chorionic gonadotropin (beta-hCG) combined with an ultrasound examination to determine the fetal nuchal translucency. The results of the first-trimester screen were revealed to study subjects only after they had also undergone a second-trimester screen consisting of the quad test (alpha fetoprotein [AFP], hCG, estriol, and inhibin) between 15 and 18 weeks of gestation. Patients were then followed to determine the outcomes of their pregnancies.
This study design allowed for accurate comparisons of the sensitivities of the 2 screening methods. An additional, critical strength of the study was the rigorous training and ongoing quality control that was demanded of those who obtained nuchal translucencies. In fact, one of the abstracts presented demonstrated very effectively the importance of treating the nuchal translucency as though it were a serum analyte. The ongoing quality-control measures used as part of the trial included onsite review of images obtained, including centralized assessments of all images acquired in the trial, and the development of center-specific medians for nuchal translucency measurements. All of these procedures had a significant impact on the quality of the measurements obtained in the study.
Among the 33,557 pregnancies, 84 carried fetuses with Down syndrome. The authors found that the first-trimester screen had an 83% sensitivity for detecting Down syndrome when the false-positive rate was 5%. This was similar to the sensitivity of the quad test, which was 79% at a similar false-positive rate of 5%, and superior to the triple screen (AFP, hCG, and estriol). For patients who opt for both the first-trimester screen and the second-trimester quad test, the sensitivity can be expected to improve to nearly 90% when the false-positive rate is 5%. With these levels of sensitivities, the triple screen by itself is no longer an acceptable alternative for Down syndrome screening -- just as the AFP test by itself is no longer considered standard of care.
Interestingly, the screening performance of the first-trimester markers in the FASTER trial varied according to the gestational age at which they were obtained. The nuchal translucency detection rate increased when it was performed at between 11 and 13 weeks of gestation, whereas the performance of PAPP-A and free beta-hCG deteriorated over the same 3-week period. Overall, the first-trimester screen functioned best when it was performed at 11 weeks of gestation. The authors did not observe a variation in performance of the individual markers used for screening for Down syndrome in the second trimester.
Other findings reported, using the database from the FASTER trial, included the following:
Medscape Ob/Gyn. 2004;9(1) © 2004 Medscape
Cite this: Highlights From The Society of Maternal-Fetal Medicine 24th Annual Clinical Meeting - Medscape - Mar 02, 2004.