Clinical implementation of noninvasive prenatal testing by Australian sonologists.

Abstract

Introduction Cell-free DNA based non-invasive prenatal testing for aneuploidy (NIPT) became available in Australia in late 2012 via overseas laboratories on a patient-funded basis. However, significant concerns existed regarding the local implementation of NIPT, including its role within the existing screening paradigm, equity of access, and the effect of overseas laboratory processing on test performance and turnaround time. This study investigated the early experience of NIPT by Australian sonologists in a national audit. Methods The study was a retrospective study of NIPT referrals for the period up to 31 December 2013 by participating ultrasound units. An online invitation distributed via email to 140 members of the Australian Association of Obstetrical and Gynaecological Ultrasonologists was sent in December 2012 inviting members to contribute de-identified patient data using a standardised data collection spreadsheet. Data were pooled so that specific information from individual practices and patients were not identifiable in the final analysis. Results Eighteen ultrasound practices in over 25 locations retrospectively collected data on their NIPT requests and submitted these for analysis. The audit period spanned August 2012 to the end of December 2013 and included data from five different NIPT providers. A combined total of 1839 NIPT requests from Victoria, New South Wales, Western Australia, and Queensland were analysed. The vast majority of tests were performed in first trimester (84.5%) in women of advanced maternal age (median 37 years). The test failure rate was 2.8% and the median turnaround time was 10 calendar days. The two most common indications for NIPT were advanced maternal age (47.7%) and a high-risk combined first trimester screening result (22.4%). Overall, 45 (2.4%) patients received a high risk NIPT result, of which 27 were high risk for trisomy 21. Thirty-five women with high risk NIPT results underwent invasive testing, of which 29 were confirmed to have an abnormal karyotype (positive predictive value = 83%). One false positive for monosomy X was attributed to low level maternal mosaicism. Approximately 1 in 100 women with a low risk NIPT result underwent invasive testing (0.9%), mostly due to a subsequently detected structural abnormality at the routine morphology scan. Conclusion This study is the first multicentre report of clinical implementation of NIPT by obstetric sonologists in Australia. It demonstrates that NIPT was predominantly used as a first trimester screen for high-risk women and produced a rational effect on downstream management. The test performance in the Australian context is consistent with the published literature.