I recommend you seek a deferral on your viva

Firstly, I'm sorry to hear of your loss. That is very sad and I hope you and your husband are able to have a child successfully in the future.

As to your academic problem, I recommend that you put in a formal request to have your viva deferred until such time as you are properly recovered from your present pregnancy-related issues. The university has standard mechanisms for students to get special consideration (including deferral of assessment items) in the event on medical issues. Fro From your description, it is clear that this event has impacted your preparation and it is still affecting you. Under such circumstances it is better to use the formal mechanisms for seeking deferrraldeferral and special consideration rather than plowingploughing ahead without these but then seeking to raise them informally. It is not unprofessional to do the latter, but it does create some problems and it is not the optimal method.

In addition to seeking a deferral, it is up to you if you want to disclose this issue directly to your examiners. You are under no obligation to disclose medical issues to staff outside of the formal process, but if you would like them to know of your circumstances then you can disclose this if you want. Many academics are parents and some have also experience miscarriages (and in any case, irrespective of whether an academic has children they will be sympathetic to your situation). No-one is going to think you are unprofessional for having experienced adverse academic impact from a pregnancy and miscarriage.