Analysis of cell-free fetal DNA in 16,843 pregnant women from a single center in China using targeted sequencing approach

Non-invasive prenatal testing (NIPT) using cell-free fetal DNA (cffDNA) has been widely accepted for detecting common fetal chromosome aneuploidies, but few large-scale studies have reported the kinetics of cffDNA concentration during gestation. This study examines cffDNA kinetics spanning gestational periods.In this retrospective cohort study, cffDNA concentration from maternal plasma of 16,843 pregnant women between 4 and 39 weeks of pregnancy were determined by SNP-based targeted deep sequencing.Maternal plasma cffDNA could be detected as early as the fourth gestational week. After detection, cffDNA concentration begun to increase to the 39th week showing three conspicuous inflection points characterized by growth and stabilization phases. The rapid increase in cffDNA (∼1.19% per week) from the 4th to 9th week represents the first growth stage. The first plateau phase spanned from the 10th to 19th week (∼0.03% increase per week). cffDNA begun to rise dramatically (∼0.85% per week) from the 19th to 29th week, stabilizing at week 30 and onwards with only 0.27% increase per week representing the second plateau period. The proportion of cases with cffDNA ≥4% increased rapidly before the 10th gestational week with no significant increase from the 10th week onwards. About 92.00% of all the maternal plasma had a cffDNA greater than 4% from 10 weeks.We indicate that cffDNA had 3 inflection points at the 10th, 19th and 30th week of gestation, an observation not yet reported. Moreover, we show that cffDNA concentration has met the NIPT requirements after 9 weeks gestational age.