The data collected by nation-wide study of noninvasive prenatal genetic testing (NIPT) for trisomy 21 from 21,610 pregnant women with advanced maternal age in Japan were reported. Among 188 NIPT-positive cases, 180 cases were true positive. The incidence of aneuploidy according to maternal age was estimated using a state-space model. Although, the frequency of trisomy increased exponentially with maternal age as previously reported, the maternal age-specific risk for trisomy 21 that was based on the clinical performance of NIPT was lower than the predicted risk in previous Western cohorts based on the data from invasive prenatal testing (Bayesian two-sided tail-area probability P = 0.0156). The empirical positive predictive value (PPV) of NIPT is likely to turn out higher than that of the theoretical PPV calculated from the sensitivity/specificity of the test and the incidence of trisomy 21 from this study.