Competing interests: KW is co-principal Investigator of the MESSAGE project which receives funding from the Wellcome Trust. No commercial or other interests. JEH receives funding from UKRI Future Leaders Fellowship MR/T040750/1. No commercial or other interests. EM reports grants from NIHR for a COVID rapid response grant, Parasol Foundation for the Blood in Action study https://www.georgeinstitute.org.uk/projects/blood-in-action; royalties from Elsevier; consulting fees from Organon and Nabla Ltd; holds a patent for Bia, a wearable uterine contraction monitor; and is a Director of Lifecourse Health Ltd, a limited company for private obstetric and anaesthetic practice.