Non-intuitive trends of fetal fraction development related to gestational age and fetal gender, and their practical implications for non-invasive prenatal testing

Abstract

Objective: Discovery of fetal cell-free DNA fragments in maternal blood revolutionized prenatal diagnostics. Although non-invasive prenatal testing (NIPT) is already a matured screening test with high specificity and sensitivity, the accurate estimation of the proportion of fetal fragments, called fetal fraction, is crucial to avoid false-negative results. Methods: We collected 6999 samples from women undergoing NIPT testing with a single male fetus to demonstrate the influence of fetal fraction by the maternal and fetal characteristics. Results: We show several fetal fraction discrepancies that contradict the generally presented conventional view. At first, the fetal fraction is not consistently rising with the maturity of the fetus due to a drop in 15 weeks of maturation. Secondly, the male samples have a lower fetal fraction than female fetuses, arguably due to the smaller gonosomal chromosomes. Finally, we discuss not only the possible reasons why this inconsistency exists but we also outline why these differences have not yet been identified and published. Conclusion: We demonstrate two non-intuitive trends to better comprehend the fetal fraction development and more precise selection of patients with sufficient fetal fraction for accurate testing.

Insights into non-informative results from non-invasive prenatal screening through gestational age, maternal BMI, and age analyses

“…A 2100 Bionalyzer (Agilent, Waldbronn, Germany) was used for quality control of final libraries. A NextSeq 500/550 platform and High Output Sequencing Kit v2 (75 cycles) (Illumina) with pair-end sequencing protocol (2 × 35 cycles) were used for sequencing [24][25][26].…”

“…In our previous study, we demonstrated that the FF of female fetuses was significantly higher than male fetuses at the same gestational age, due to the smaller gonosome Y/chromosome Y and biological differences between the sexes. We also observed that the FF does not grow consistently with fetal maturity due to a drop in 15 weeks of gestation [ 24 ]. The objective of the present study was to analyze the data of 5543 pregnant women who underwent NIPT in the Slovak population including 189 repeated sampling and following analysis due to insufficient FF of the first sampling.…”