There are many people replying to this thread not knowing anything about what they are writing. (Besides
@AT_1)
You do not need to inform IRCC of pregnancy. Plain and simple. You can't add someone to an application who hasn't been born and your POF is only needed for 2 people.
You can get medicals done, just tell the panel doctor that your wife is pregnant, and she will be excused from doing the X-ray, which can be dangerous for the baby.