Randomisation and masking
PTB
Women were randomly assigned in a 1:1 ratio via a secure web-based system (MedSciNet) to the intervention (POPPIE group) or control arm (standard group). A minimisation algorithm was used to ensure balance between the groups regarding previous PTB and smoking at booking. Blinding of participants and HCPs could not be achieved due to the nature of the intervention. However, study allocation was blinded to the statistician and the researchers who analysed the data [