Analysis of three different strategies in prenatal screening for Down's syndrome in twin pregnancies.

ABSTRACT

OBJECTIVES: To compare the performance of three different strategies in prenatal screening for Down's syndrome in twins [nuchal translucency, the combined test, the combined test + ductus venosus pulsatility index (DVPI)]. METHODS: We included 277 twin pregnancies with two cases of trisomy 21 (both dichorionic). We performed a computer simulation of Down's syndrome NT screening, combined test screening and the combined test with the addition of DVPI screening using the commercialized software SsdwLab6. The strategies were compared using the area under the receiver operating characteristic curve. RESULTS: NT screening false-positive rate (FPR) was 10.9% (95% CI 8.3-13.5). The combined test FPR was 6.2% (95% CI 4.1-8.2%) and the combined test plus DVPI was 6% (95% CI 4-8). FPR was higher in advanced maternal age patients. Detection rate was 100% in all cases. The area under the curve was 0.987 (95% CI 0.972-0.994) in NT screening; 0.987 (95% CI 0.978-0.997) in the combined test and 0.983 (95% CI 0.977-0.996) in the combined test + DVPI. CONCLUSIONS: Down's syndrome screening is feasible in twins with low FPR. The results of this study are similar to the results achieved in singletons. The combined test appears to be the most effective. The addition of DVIP does not significantly improve the prenatal screening for trisomy 21.