First off Congratulations on this good news. Secondly, please be truthful with CIC and don't try to conceal any information because in case let's say (I hope this does not happen, but just a thought) they issue a PR visa after 9 months, then they will only issue it to your wife and not to your child leading to unwanted complications. Even if it takes time for them to issue the visa ensure that it's done the right way.
Pros: Well, now that you will have a kid in your family, this proves further that your relationship is genuine and your wife may get an unconditional visa (read up CIC's site for more information) there by not having to worry about contacting CIC after 2 years (to change the status from conditional to unconditional; which means saving some moolah
)
Cons: It could take some time before the visa may be issued. But overall I would not worry about the cons for now. I would only worry during the 8-9th month (in case CIC has not cleared your file).
Good luck and disclose the facts to them in your welfare (I think you can ask your wife to send all the required documents about your visit to India, her medical conditions etc., to the NDVO office).
Cheers!