Comparison of noninvasive prenatal screening with combined first-trimester screening as a frontline screening approach for common trisomies in a public hospital in Australia.

BACKGROUND

Combined first-trimester screening (cFTS) for fetal anomalies involves maternal serum screening for biochemical markers and measurement of the nuchal translucency (NT) by ultrasound. Noninvasive prenatal screening (NIPS) analyses cell-free DNA present in a maternal blood sample for presence of fetal chromosomal aneuploidies.

AIMS

To compare NIPS with cFTS as frontline screening in a public hospital in Australia.

MATERIALS AND METHODS

Women were offered NIPS in addition to the usual cFTS routinely offered to all women at a public hospital in NSW, Australia. The cFTS sample was collected at ten weeks' gestation and the NIPS sample at 12 weeks' gestation at the ultrasound appointment.

RESULTS

In a low-risk population of 997 women, frontline NIPS had a screen-positive rate of 0.5% (5/997) vs 4.2% (42/997) with cFTS. cFTS correctly identified one trisomy 21 case and one trisomy 18 case; however, there were two trisomy 18 false negatives. Of five positive NIPS calls, four were correctly identified as trisomy 21 (one) and trisomy 18 (three); there were no NIPS false negatives. Overall, the false-positive rate with NIPS was 0.1% vs 4.0% by cFTS.

CONCLUSIONS

The lower screen-positive rate with NIPS for common trisomies was a result of the significantly lower false-positive rate with NIPS. Consequently, NIPS as first-line screening, even if funded by the hospital, may provide cost savings. We believe NIPS should be used from ten weeks' gestation in conjunction with morphology ultrasound for routine first-trimester prenatal management.