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.