Funding for this research was provided by:
Economic and Social Research Council (150041616)
Medical Research Council (MR/K501396/1)
Wellcome Trust (WT101597MA)
National Institute for Health Research (IS-CLA-0113-10020)
Received: 18 March 2020
Accepted: 7 July 2020
First Online: 1 September 2020
Ethics approval and consent to participate
: BiB have ethics approval from Bradford Research Ethics Committee for the data to be collected and used for research purposes (REC reference number: 07/H1302/112). Approval of data sharing and collaboration from BiB was received on 07/03/19 which was an addendum to a previous application (ID SP48).
: Not applicable.
: The authors declare that they have no competing interests. Nicola Heslehurst is a member of the editorial board of BMC Pregnancy & Childbirth. All other authors declare no competing interests.