Noninvasive prenatal screening using dynamic iterative depth optimization with depth-scaled variance determination

Abstract

Fetal maternal samples taken from pregnant women include both maternal cell-free DNA and fetal cell-free DNA. Described herein are methods for determining a chromosomal abnormality of a test chromosome in a fetus by analyzing a test maternal sample of a woman carrying said fetus, wherein the test maternal sample comprises fetal cell-free DNA and maternal cell-free DNA. The chromosomal abnormality can be, for example, aneuploidy or the presence of a microdeletion. In some embodiments, the chromosomal abnormality is determined by measuring a dosage of the test chromosome, determining a depth-scaled variation value correlated to an initial number of sequencing reads obtained from an assay of the test maternal sample, and determining an initial value of statistical significance for the test chromosome based on the measured dosage of the test chromosome, an expected dosage of the test chromosome, and the depth-scaled variation value.