Chromosome trisomy risk calculation
Sequencing data were analyzed using a binary hypothesis T-score as
previously described [19]. Briefly, a binary hypothesis T-test and
logarithmic likelihood ratio L-score between the two t-tests were used
to classify whether the fetuses had T21, T18 or T13. T-score higher than
3 was used as the cut-off to identify fetal trisomy, and L-score higher
than 1 was used to determine the confidence.