It seems that our experiences have been pretty similar We'd also been hoping to have the via approved before the birth to qualify for PPL, but I'm not certain that we would qualify even it it were granted. I'm not sure if PPL payments come under the Newly Arrived Residents Waiting Periods, or not. We've been told a number of conflicting stories http://www.humanservices.gov.au/customer/enablers/newly-arrived-residents-waiting-period
My other half is also from a low-risk, and Medibank said that the X-ray can be deferred until after the birth, but neither them nor the case officer would give a clear answer as to what that actually means for visa application. At this stage, I feel doubtful it will be granted until after the birth. If that's the case, then I think it becomes necessary to submit a change of situation on the application and likely becomes necessary to pay the extra applicant fee for the child