Received: 7 October 2020
Accepted: 16 March 2021
First Online: 26 March 2021
Change Date: 19 May 2021
Change Type: Correction
Change Details: A Correction to this paper has been published:
Change Details: https://doi.org/10.1186/S12884-021-03871-W
: For the data used in the is study, section 251 approval was granted by the Health Research Authority Confidentiality Advisory Group to process patient identifiable information without consent for the purposes of service evaluation (16/CAG/0058). This study was therefore exempt from ethical review by the National Health Service Health Research Authority.
: We have no competing interests to declare.