I hadn't realised that in addition to the UKMEC there is a USMEC and a WHOMEC, all produced in a similar fashion using the latest evidence. Given that "it's all about safety", are the recommendations in all these MECs the same? If not, why?
The WHOMEC is primarily intended for use in developing countries where the risks associated with pregnancy are often extremely high but it is the intention of WHO that the guidance be adapted for use in different settings in which the risk benefit ratio of contraceptive methods may differ. The USMEC and UKMEC are two examples where the WHOMEC has been adapted to be applied to the different countries/settings.
For many conditions there is an absence of robust evidence (eg. multicentre randomised controlled trials or even large observational studies), or the quality of evidence is low or conflicting. In such circumstances expert opinion with consensus will be used.