Conclusion: There is nothing wrong with you studying medicine and working as a doctor, whilst taking precautions to avoid matters concerning which there are shar‘i reservations. In fact, studying medicine is a beneficial field of knowledge, by means of which one may benefit and help people.

Conclusion: if the scalp is injected with plasma, that does not invalidate the fast. That is in contrast to injection of blood via a vein, which takes the place of food and drink, so the fast is invalidated thereby.

based on that, if trustworthy doctors have stated that pregnancy would result in considerable harm to your wife, it is permissible to take measures to prevent pregnancy. And Allah knows best.