Comparison of the efficiency of second-trimester nasal bone hypoplasia and increased nuchal fold in Down syndrome screening.

OBJECTIVE: The purpose of this study was to compare the efficiency of second-trimester nasal bone hypoplasia (NB) and increased nuchal fold (NF) in Down syndrome screening. STUDY
DESIGN: This was a prospective multicenter cohort study of women who underwent an anatomic survey between 16 and 22 weeks of gestation. The fetal NB and other markers of fetal aneuploidy that included NF were evaluated. NB was defined either as an absent NB or length of <0.75 multiples of the median for the gestational age. Two definitions of increased NF (>5 mm and >6 mm) were evaluated. Fetuses or infants with Down syndrome were compared with those fetuses without for the presence of NB and increased NF.
RESULTS: Among 4373 pregnancies that were evaluated over a 5-year period, there were 50 pregnancies with Down syndrome. NB evaluation was obtained in 3936 of 4373 pregnancies (90%); NF was evaluated in all of the fetuses. Absent NB was seen in 14/49 cases (29%), and NF of >6 mm was seen in 6 of 50 cases (12%) with Down syndrome.
CONCLUSION: Nasal bone and nuchal fold are efficient markers for Down syndrome. Absent nasal bone was a better predictor of Down syndrome, compared with nuchal fold, and should be a standard marker when a second-trimester genetic sonogram is performed.