OP08.05: Factors affecting fetal fraction in 5,103 cases of a mixed Australian population

To examine potential biological factors affecting the fetal fraction (FF) of cell-free DNA in maternal plasma using non-invasive prenatal testing (NIPT) in an Australian mixed-risk population. Data from 5,103 women who had NIPT across three private practices specialising in obstetric ultrasound and prenatal diagnosis in Australia were combined. Multivariable regression analysis was used to determine whether maternal characteristics, ultrasound information, or placental biomarkers affect FF. FF results were available for all women in the sample and ranged from 4% to 37% (mean 11.6, SD 4.3%). Body mass index (BMI) and gestation were found to be the most significant factors associated with FF. For each unit increase in BMI, the logarithmically transformed FF (logFF) mean value decreased by 0.031 (95%CI: 0.028, 0.034). Conversely, each week increase in gestation, logFF increased by 0.025 (95%CI: 0.021, 0.030). Maternal age and placental biomarkers were found to be significant predictors of FF, although less than BMI and gestation. For each year increase in maternal age, the logFF decreased by 0.006 (95%CI: 0.004, 0.009). Conversely, for each unit increase in free BhCG, PAPPA and PlGF the logFF increased by 0.082 (95%CI: 0.062, 0.101), 0.087 (95%CI: 0.061, 0.113) and 0.16 (95%CI: 0.07, 0.24) respectively. There was no significant association between nuchal translucency (NT) thickness and FF (p = 0.19). MAP and uterine artery PI were negatively correlated with FF. The fetal fraction in maternal plasma cfDNA increased with gestational age, serum PAPP-A, β-hCG and PlGF and decreased with maternal weight, MAP and uterine artery PI. There was no significant association with NT.