An audit of first trimester ultrasound screening for chromosomal abnormalities

Screening for Down syndrome has been funded in New Zealand since 2010 following the report 'Antenatal Down Syndrome Screening in NZ 2007' which identified that the practice of screening using maternal age and/or nuchal translucency (NT) without biochemical markers was unsafe and should not continue.

This study aimed to assess the quality of the ultrasound component of first trimester screening in a metropolitan population.

Over a 5-month period, all available NT scan images for women referred to the Central Region Fetal Medicine Unit for an increased risk at first trimester screening or a fetal abnormality detected at the 20-week ultrasound scan were reviewed according to the Fetal Medicine Foundation (FMF) criteria and utilising the Herman Score. This is the standard which the National Screening Unit (NSU) and Ministry of Health (MOH) have mandated for the ultrasound component of the screening test.

Of the 52 images, 4 (7.7%) studies were considered unacceptable and another 5 (9.6%) were considered intermediate. The mean score was 5.87 of a possible score of 9. Comparisons with Herman's data are presented and discussed.

This review suggests that there is potential for the quality of the ultrasound component of the first trimester screening component to improve. This would in turn improve the performance of the screening program. We conclude that formal quality control of this screening program is urgently required.