Congrats for the baby!!!
I don't think your application will be effected or delayed by your relationship status change; however you need to inform CIC about it and the baby. You will have to send the updated family form and birth certificate for the baby. Since your partner and baby r both Canadian you don't need to add them to your application.
I suggest email CIC about the changes in your family and they will instruct you to fill the necessary forms. Inform ASAP