Cribado de aneuploidía en gestación gemelar: resultados de la aplicación del test combinado

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

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.

First trimester risk assessment for trisomy 21 in twin pregnancies combining nuchal translucency and first trimester biochemical markers

OBJECTIVE

The aim is to describe the performance of first-trimester combined risk assessment in twin pregnancies.

METHODS

Maternal serum free beta-human chorionic gonadotrophin and pregnancy-associated plasma protein A (PAPP-A) were determined at 8 to 12 weeks and fetal nuchal translucency (NT) was measured at 11 to 13+6 weeks. The individual risk was estimated for each fetus using the combined test in dichorionic twins. In monochorionic twins, the mean risk assessment of the two fetuses was used. An invasive diagnostic procedure was offered when the risk was ≥ 1 : 270 in either one of the fetuses.

RESULTS

From February 2007 to June 2011, 447 twin pregnancies were enrolled in this study. There were 402 (89.9%) dichorionic and 45 (10.1%) monochorionic twins. In dichorionic twins, mean crown-rump length (CRL) was 63.9 mm; median NT multiples of the median (MoM) was 0.97; median Β-hCG was MoM 1.74; median PAPP-A was 1.72. In monochorionic twins, mean CRL was 61.9 mm; median NT MoM was 0. 98; median Β-hCG MoM was 1.44; and median PAPP-A was 1.51. Two pregnancies with Down syndrome were detected by first trimester screening, both in dichorionic twins. The false positive rate was 5.7% (95% confidence interval 4.1-7.3) and 4.4% (95% confidence interval 0.1-8.8%) in dichorionic and monochorionic twins, respectively.

CONCLUSIONS

The combined test in twins appears to be a good method for Down syndrome screening with a high detection rate and an acceptable false-positive rate.