Background

Queensland introduced a colour-coded cardiotocograph (CTG) classification system (green, blue, yellow and red) to complement the Royal Australian and New Zealand College of Obstetricians and Gynaecologists prose-based classification system of ‘low, unlikely, maybe or likely’ fetal compromise.

Aims

The aim of the study was to determine the clinical impact of the introduction of the colour-coded CTG classification system compared to the prose-based system. We hypothesised there would be no change in the rate of operative delivery for intrapartum fetal compromise (OD-IFC).

Materials and methods

This retrospective non-inferiority study from November 2014 to May 2018 used routinely collected data from the Mater Mother’s Hospital. Non-insured women with a singleton, non-anomalous, cephalic fetus at term, attempting a vaginal birth with continuous intrapartum CTG were included. The primary outcome was OD-IFC. Secondary outcomes included various obstetric and perinatal outcomes. Non-inferiority analysis was performed with a pre-specified non-inferiority margin of 2% risk difference.

Results

Eleven thousand seven hundred and twenty-seven participants were included. The OD-IFC rate was similar across the study groups (prose-based 15.1% vs colour-coded 15.3%, adjusted odds ratio (aOR) 1.02, 95% CI 0.93–1.13) with the adjusted risk difference of 0.29% (95% CI −0.98 to 1.56), which did not exceed the inferiority margin. There were more spontaneous (aOR 1.11, 95% CI 1.04–1.19) and fewer instrumental (aOR 0.87, 95% CI 0.80–0.95) vaginal births in the colour-coded cohort. There were no differences in neonatal outcomes.

Conclusions

Reassuringly, the colour-coded CTG classification system was non-inferior to the prose-based system, did not influence OD-IFC but was associated with more spontaneous vaginal deliveries.