Objective:

To study factors that influence the concentration of cell-free fetal DNA (fetal fraction) using a large clinical data set of pregnancies with male fetus.

Method:

A retrospective analysis of 23 067 pregnancies that received noninvasive prenatal testing from January 2012 to October 2013, including 22 650 normal singleton pregnancies (control group) and 417 pregnancies with aneuploidy, twin pregnancy, or various maternal conditions including preexisting hypertension, preexisting diabetes, hyperthyroidism, and carrier of the surface antigen of the hepatitis B virus (HBsAg; study group). Multiples of the median (MoM) analysis was performed in the control group to derive gestation and body mass index (BMI)-corrected fetal fraction. The effects of study group conditions on fetal fraction were examined by calculating the ratio of MoM (RMoM) values.

Results:

Fetal fraction showed a positive correlation with gestational age (r² = .10, P < .001) and increased rapidly after the 21 weeks of gestation (r² = .26, P < .001). Negative association with maternal BMI was found with fetal fraction (r² = .04, P < .001). In study group, fetal fraction was higher among pregnant women with a trisomy 21 fetus (RMoM = 1.24, P < .001) and lower among trisomy 18 (RMoM = 0.84, P < .001). A 1.6-fold incensement of fetal fraction was observed in twin fetuses comparing to singleton pregnancy (RMoM = 1.62, P < .001). Women with preexisting hypertension had significantly lower fetal fraction (RMoM = 0.85, P = .02). Preexisting diabetes, hyperthyroidism, or carrier of HBsAg did not affect fetal fraction.

Conclusion:

The fetal fraction was affected by fetal aneuploidy, maternal BMI, and the number of gestation. Maternal preexisting of hypertension appeared to reduce fetal fraction.