How would you approach this situation?

Looking for some advice?

I had a private discussion about a new role in the department I work in now, but working in a different team under a new manager. I had a chat with the hiring manager to express that I’m really interested but wanted to get more information about the role before I definitely applied, I get on with this manager personally also so it was a fairly informal chat but I hadn’t discussed it with my current manager yet and she confirmed she’d keep our discussion private until I decided what I want to do and we could then have a 3 way discussion.

I’ve just found out I’m pregnant, so moving wouldn’t be a sensible option now because it was only a fixed term job for 12 months so it would have meant a secondment from what I do now. So to move knowing I’m pregnant would be a headache for everyone involved (including me having to learn a new job) but I don’t know how to politely decline my interest in applying without it being somewhat obvious I’m pregnant because it’s still early days really (I’m about 7 weeks).

I have a lot of respect for this manager and I know if I confided the real reason for changing my mind she’d remain confidential and would completely understand, but then I feel guilty that I’d be essentially notifying a manager that isn’t my own about being pregnant. I wouldn’t look to have that conversation with my own manager until I was closer to 12 weeks.

If you were in my position, what would you do?