New job

I start a new job on tuesday and found out I am 6 weeks pregnant. what do I do!! I'm on a 3 mnths probation. I know they can't fire me for being pregnant but here in Canada they can let me go regardless in the first 3 months for no reason at all.. do I hide it until 3 mnths which makes me 4 mnths (note I'm already showing) or is honesty the best policy?!?!?!