Association between cell-free DNA fetal fraction and pregnant character: a retrospective cohort study of 27,793 maternal plasmas

To determine the association between cell-free DNA fetal fraction (cffDNA) and various prenatal characters to better guide the clinical application of noninvasive prenatal screening (NIPS), a retrospective cohort study of 27,793 women with singleton pregnancies was conducted. Results indicated that no significant difference on cffDNA between trisomy/sex chromosome aneuploidy (SCA) and non-trisomy groups was found. However, the fetal fraction (FF) in the T18 and T13 subgroups were significantly lower than that in the non-trisomy group, while the FF in the T21 group was significantly higher than the non-trisomy group. Pearson's correlation analysis revealed a positive correlation between √FF and gestational week in the T21, SCA, and non-trisomy groups. A negative correlation between maternal age and √FF in T21 and non-trisomy cases was found, but a positive correlation in SCA group. Compared to the decreasing trend in FF in the T21 group, no significant difference was observed in the SCA group. The √FF level was negatively correlated to maternal BMI in T21 and non-trisomy group, while a positive correlation in SCA group. FF was close related to the result of NIPS and related maternal factors. Though NIPS has increased accuracy, the complexity still should be recognized especially in clinical practice.