@LilCritter even if you are in probation if the FIRST time you hear about any concerns about your skills or performance is at the end of your probation period and they let you go, and you believe it's because you are pregnant then you should absolutely lodge a discrimination claim. They need to have told you before and given you the chance to improve.

Employees do have rights during probation but most assume they don't so employers take advantage.

The onus is on them, not you, to prove that discrimination didn't take place and if they have no records of any issues with your performance it's unlikely they will be able to prove it.