When did you tell your employer (at your new job) that you’re pregnant?

Should I wait until after the probation period? I know it’s illegal to fire someone because they’re pregnant but I feel like they could come up with any dumb excuse during the probation period to let me go without any legal trouble.

My only concern is that I’m already 12 weeks and growing so by the end of probation period, it might be obvious!

My first day is tomorrow and I was told that my boss (who I will be meeting tomorrow) is very strict and hard to get along with...which makes me really excited to tell him this news :/