Relationship between core implementation outcomes and the primary outcome
PTB
The effect of the intervention on the primary composite outcome was similar in the POPPIE group and standard group (RR 0.98; 0.90 to 1.08). After planned adjustments for important measurements associated with PTB (ethnicity, parity, education, deprivation, obstetric risk), no significant benefit of the intervention was found. None of the high- or low- fidelity and acceptability implementation measures were associated to the primary outcome. When measures were aggregated into a composite score, the combination of high fidelity and acceptability and low fidelity and acceptability were not significantly associated with the primary outcome (RR 1.21; 0.73 to 2.01 and RR 0.82; 0.49 to 1.35 respectively). The relationship between implementation measures and the primary outcome is detailed in 