Screen-positive rate in cell free DNA screening for microdeletion 22q11.2.

OBJECTIVE: To examine the impact of the fetal fraction on the screen-positive rate in screening for microdeletion 22q11.2.

METHODS: This study is based on samples that were analyzed using the Harmony® Prenatal Test (Roche Inc, San Jose, California). The study cohort comprised of samples from women with singleton pregnancies who were at least 16 years old and at least at 11 weeks' gestation. Logistic regression analysis was used to determine significant covariates that carry an impact on the screen-positive rate.

RESULTS: The study population consisted of 52,019 pregnancies including 309 pregnancies with a high risk result for microdeletion 22q11.2. Thus, the overall screen-positive rate was 0.59%. In the low risk group, the fetal fraction was 10.1% and in the high risk group, it was 7.3%. Regression analysis indicated a strong correlation between the fetal fraction (FF) and the screen-positive rate. In the cases with a FF of less than 11.0%, the screen-positive rate was 0.92% while it was 0.13% in the group with a higher FF.

CONCLUSION: The screen-positive rate depends on the fetal fraction. In order to keep the rate low, we recommend restricting the analysis to samples with a fetal fraction of 11% and more. This article is protected by copyright. All rights reserved.