The baby doesnt provide you with any special status. You can apply common-law (if you qualify) or you can get married. The baby will help a little bit in proving the relationship is genuine, but thats about it.
Even if you submit the application today, it is unlikely the entire process will be completed in less than 5 months, so whatever you do, she will not be a PR when the baby is born. Just include it as a dependant in the application.