Objective      To evaluate the detection rate of massively parallel sequencing (MPS)-based screening for chromosome abnormality of fetus free DNAs in their mother’s plasma

and provide clinical data for this non-invasive prenatal screening.       Methods      A total of 5 997 pregnant women with an age from 18 to 46 and a gestational age from 12 to 36 weeks who receiving prenatal examination in our center from June 2011 to November 2012 were recruited in this study. Five milliliters of peripheral blood were collected

and then the fetus DNAs were extracted from mother plasma and barcoded. The libraries of each sample were pooled and subjected to Illumina GAⅡx analyzer. Short reads were analyzed by binary hypothesized t tests and L-score analysis. Positive results of MPS were validated by cordocentesis based karyotyping.       Results      A total of 113 patients were found to be abnormal by MPS. Among them

89 mothers accepted cordocentesis based karyotyping

and the obtained sensitivity for trisomy 21 and trisomy 18 were 100% (28/28) and 87.5% (7/8)

respectively. However

the sensitivity for sex chromosome abnormality was 33.3% (14/42). Routine screening for Down’s syndrome showed a false negative ratio of 11.8% (2/17)

while MPS had no false ratio. The age (P=0.261) and gestational weeks (P=0.309) had no significant effect on the detection rates of MPS.       Conclusion      Non-invasive MPS screening is a more reliable detection for trisomy 21 than conventional routine screening for Down’s syndrome

and is suitable for large-scale screening for trisomy 21 to reduce the ratio of invasive cordocentesis based karyotyping.