Objective
To evaluate the performance of non-invasive prenatal testing for all fetal chromosomal aneuploidies in an extremely high-risk group undergoing first-trimester combined Down syndrome screening.

Method
A multicentre cohort prospective study in Taiwan was performed between June and December 2012. Maternal plasma was collected and shotgun massive parallel sequencing was performed on each fetal chromosome. Two hundred one Taiwanese pregnant women at > 12 weeks gestation from 11 medical centers were enrolled in this trial. The extremely high-risk group was defined as a Down syndrome risk cut-off > 1:30 or nuchal translucency > 3.0 mm (n=100), while the low-risk group was defined as a Down syndrome cut-off < 1:1500 (n=101). Amniocentesis confirmation was performed and birth outcome was also recorded.

Results
There were 11 cases of trisomy 21, 8 cases of trisomy 18, 3 cases of trisomy 13, 1 case of trisomy 16, 3 cases of 45,XO, and 1 case of 47,XYY detected prenatally in 100 extremely high-risk gravidas (n=27/100 [27%]). The overall autosomal or sex chromosome aneuploidy detection rate was 96% (27/28) because of an insufficient amount maternal plasma for one fetus with Turner syndrome. In the low-risk group, no chromosomal abnormalities were detected (specificity=100%). There were no false-positive cases in this study.

Conclusions
This first trial in Taiwan showed that non-invasive prenatal testing for whole chromosome aneuploidies can be efficiently applied in extremely high- or low-risk populations.