First of all congratulations.
Good question too - I did this - ie quit soon after we found out wife was pregnant.
Given the state of the mkt right now, wait til baby is born and only then start looking. Maybe even build up a nest egg now.
Don't assume that just cos you've got a kid the career will end straight away, I'd suggest to try and make it work first. The first few weeks/months as a parent will be tough whether you're working in MC or not. If you change now you'll be only a few months into a new job, or possibly still unemployed.
Second time round (2nd baby) I stayed with the consultancy throughout and it worked out well