We are unable to issue letters/certificates stating patients are “fit to fly”. Assessing whether someone can fly falls outside our area of expertise as General Practitioners (GPs).
Your hospital team will be better placed than us to inform your airline of some conditions. Pregnant women may be able to obtain the required paperwork from their obstetrician.
The UK Civil Aviation Authority states:
“Most airlines have medical advisors who advise and clear passengers as fit to fly. The final decision on whether or not to carry a passenger is that of the airline