You cannot let them know about something that did not happen yet. Change in health does not include pregnancy, from what I know. Ideally you should try to land as soon as you receive the passport (with visa and CoPR). In case you cannot do that and you want to add the newborn to the application, I believe that the procedure would be revoke your CoPR, add the new family member and issue new CoPR for all of you.I expect passports back around early March. Her delivery is late April and our medical expires April 19th. That leaves us a tiny window of 2 weeks mid March to land. If we can't travel, would there be any backslash from IRCC, something like "Oh, we can't reissue your PPR cuz you failed to let us know about the baby delivery " ?
I would wait for someone more expert than me (@legalfalcon ) on this matter, but this is my opinion.