Noninvasive prenatal testing in routine clinical practice--an audit of NIPT and combined first-trimester screening in an unselected Australian population.

BACKGROUND: There are limited data regarding noninvasive prenatal testing (NIPT) in low-risk populations, and the ideal aneuploidy screening model for a pregnant population has yet to be established. AIMS: To assess the implementation of NIPT into clinical practice utilising both first- and second-line screening models. MATERIALS AND METHODS: Three private practices specialising in obstetric ultrasound and prenatal diagnosis in Australia offered NIPT as a first-line test, ideally followed by combined first-trimester screening (cFTS), or as a second-line test following cFTS, particularly in those with a calculated risk between 1:50 and 1:1000. RESULTS: NIPT screening was performed in 5267 women and as a first-line screening method in 3359 (63.8%). Trisomies 21 and 13 detection was 100% and 88% for trisomy 18. Of cases with known karyotypes, the positive predictive value (PPV) of the test was highest for trisomy 21 (97.7%) and lowest for monosomy X (25%). Ultrasound detection of fetal structural abnormality resulted in the detection of five additional chromosome abnormalities, two of which had high-risk cFTS results. For all chromosomal abnormalities, NIPT alone detected 93.4%, a contingent model detected 81.8% (P = 0.097), and cFTS alone detected 65.9% (P < 0.005). CONCLUSIONS: NIPT achieved 100% T21 detection and had a higher DR of all aneuploidy when used as a first-line test. Given the false-positive rate for all aneuploidies, NIPT is an advanced screening test, rather than a diagnostic test. The benefit of additional cFTS was the detection of fetal structural abnormalities and some unusual chromosomal abnormalities.