Factors associated with obtaining results on repeat cell-free DNA testing in samples redrawn due to insufficient...

Objectives: To investigate factors associated with obtaining results on repeat cell-free DNA testing for fetal trisomy after an initial sample with insufficient fetal fraction.Methods: A series of clinical laboratory samples was queried to identify patients with multiple samples drawn for the Harmony^® prenatal test. Maternal demographics, gestational age, timing of sampling, and repeat test outcome were reviewed. Multivariate logistic regression analysis was used to determine the odds ratio of obtaining a result.Results: Two thousand nine hundred six unique pregnancies were identified with a sample submitted for repeat testing after an initial test with an insufficient fetal fraction. Overall, 53% obtained a result on the second draw. The odds of obtaining a result were associated with interval time between draws (per day, OR 1.040, 95% CI 1.031-1.051) and maternal weight (per kg, OR 0.988, 95% CI 0.985-0.991) but not maternal age, gestational age at initial draw, IVF status, or twin versus singleton pregnancy.Conclusions: The probability of obtaining a result with repeat cell-free DNA testing decreases with higher maternal weight and increases with the interval between draws. Waiting longer before collecting a repeat sample increases the probability of obtaining a result but should be considered in the context of the gestational age of the pregnancy and the clinical indication for testing.