Screening for Down syndrome using first-trimester ultrasound and second-trimester maternal serum markers in a low-risk population: a prospective longitudinal study
F. Audibert et al., Screening for Down syndrome using first-trimester ultrasound and second-trimester maternal serum markers in a low-risk population: a prospective longitudinal study, ULTRASOUN O, 18(1), 2001, pp. 26-31
Objectives To compare nuchal translucency and second-trimester maternal ser
um measurements as alternative methods of antenatal screening for Down synd
rome in a low-risk population and to evaluate the consequence of combining
the results in the estimation of risk.
Design In a consecutive series of 4130 women aged less than 38 years with a
singleton pregnancy, we examined both the detection rate of Down syndrome
by nuchal translucency measurement at 10-14 weeks and maternal serum screen
ing by human chorionic gonadotrophin and alpha-fetoprotein at 14-18 weeks.
Women with a nuchal translucency, measurement of greater than or equal to3
mm and women with a maternal serum screening-derived risk greater than or e
qual to 1/250 were recommended to have amniocentesis. A second-trimester de
tailed ultrasound scan was also performed in all women. The outcome of all
pregnancies was recorded prospectively and the detection rate and false-pos
itive rate of different screening strategies were retrospectively analyzed.
Results Out of the 4130 pregnancies that were followed (mean maternal age,
30.1 years), 12 cases of Down syndrome were observed (0.28%), all detected
prenatally. Seven of 12 cases had a nuchal translucency measurement of grea
ter than or equal to3 mm (58%), and six out of 10 cases with available mate
rnal serum screening had a calculated risk of greater than or equal to 1/25
0 (60%). Four of the five Down syndrome cases with a nuchal translucency me
asurement of < 3 mm were detected by subsequent maternal serum screening. A
t a threshold giving 5% of positive tests, the sensitivity of nuchal transl
ucency, maternal serum screening and combined risk screening were 75%, 60%
and 90%, respectively.
Conclusions In screening for Down syndrome, an approach which combines the
results from first-trimester nuchal translucency and second-trimester bioch
emistry, is effective and increases the detection rate compared to the use
of any single test. However, this strategy is likely to raise the false-pos
itive rate and the interpretation of maternal serum screening-derived risk
should be combined with the first-trimester nuchal translucency measurement
.