If I were you, I would call CIC to find out how I can add spouse as co-signer for the sponsorship undertaking due to the status change and, if that could be reinstated to be effective any date after you got married, better back in the year when you were on the MAT leave. I wouldn't mention anything other than that for the moment unless I really needed to, especially the personal finanical situation, etc. I suggest you to do it as quickly as possible considering that you might be requested by CIC to update your financial status for the past 3 years. The worst case scenario I could imagine would just have your case delayed to the point until your status being updated, ie. have your husband added as a co-signer, it should not bounce your case off to the beginning.
Actually, you MUST update CIC of your status change, because the income threshold being applied to your case would be changed to base on 3 ppl, you, your husband and your baby. What's the most important thing is to find out how you can add your husband as a co-signer to ensure the income from both your and your spouse satisfies financial requirement for sponsorship.