The objective of this study was to evaluate the accuracy of non-invasive detection of fetal trisomy 18 using the unmethylated-maspin (U-maspin) gene as a cell-free fetal DNA marker and the methylated-maspin (M-maspin) gene as a cell-free total DNA marker in maternal plasma during the first trimester of pregnancy. Here, SERPINB5 is linked to trisomy 18.