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.
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.
Authors: Peter G Scheffer; Soetinah A M Wirjosoekarto; Ellis C Becking; Marjan M Weiss; Caroline J Bax; Dick Oepkes; Erik A Sistermans; Lidewij Henneman; Mireille N Bekker Journal: Prenat Diagn Date: 2021-08-18 Impact factor: 3.242