When placental and fetal karyotypes were both available and determined to be discordant, NIPT findings were considered TP if they matched the fetal karyotype, and FP if they did not match the fetal karyotype. Pregnancies were considered mosaic when chromosome analysis revealed either placental or fetal mosaicism or there was discordance between placental and fetal karyotypes. Patient and sample characteristics were expressed as means, SD, medians, and ranges. Linear regression analysis
was used to determine the relationship between fetal fraction find more and gestational age, between fetal fraction and maternal weight, and between fetal/maternal cfDNA and maternal weight; a reciprocal model was used when determining GSK126 ic50 the relationship between fetal fraction and gestational age or maternal weight. For comparison
of euploid and aneuploid calls, fetal fractions were expressed as multiples of the median (MoM) relative to low-risk calls weighted by week of gestation, and significance determined using a Mann-Whitney rank sum test. The 2 FN results were included in the appropriate aneuploid category, and FP calls were excluded from aneuploidy fetal fraction analyses. The benefit
of a paternal sample on redraw rates and differences the in aneuploidy incidence between the a priori risk groups were determined using a χ2 test. The Kruskal-Wallis 1-way analysis of variance on ranks test was used to evaluate maternal age and gestational age differences for the different risk groups. Positive predictive value (PPV) ([TP]/[TP + FP]) was calculated for cases with known cytogenetic analyses. SigmaPlot 12.5 (Systat Software, San Jose, CA) was used for all statistical analyses. P < .05 was considered statistically significant. Patient and sample characteristics for the 31,030 cases received during the study period are detailed in Table 1. Mean maternal age was 33.3 years, with 51.4% (15,952) aged ≥35 years at the estimated date of delivery. Mean gestational age was 14.0 weeks, with 64.5% (20,001) of samples drawn in first trimester and 33.8% (10,479) in the second trimester. Figure 1 depicts the study flow chart.