Follow up
Women in the POPPIE and standard groups who had a live birth and did not withdraw from the trial were followed up at six-eight weeks postpartum (or until discharge from neonatal intensive care unit up to three months). They were invited to complete a postnatal survey and participate in interviews based on a maximum variation sampling strategy [HCPs (frontline staff such as midwives, doctors) and other key stakeholders (i.e. senior management from the hospital, the local Authority, the Clinical Commissioning Group, Maternity Voices Partnership) involved in the development and/or delivery of the intervention were also invited to take part in a qualitative interview during mid and post-implementation. Both HCPs and stakeholders were recruited by non-clinical members of the research team using a snowballing approach through researchers’ and collaborators’ contacts. They were purposively selected to ensure participants were from different maternity settings, professional roles, and seniority levels.