S.H.
I'm sorry - what a pita this must be for you. I think it's a good idea for you to ask them which chemicals will be used and then research those particular chemicals. Unfortunately I suspect that you won't be able to stop them or even delay them from doing the extermination. I'm not sure what your lease states, but most leases have a clause directly related to extermination stating that the landlord is entitled to do so when they deem necessary. If your lease doesn't specifically address extermination then you may be able to negotiate with them to delay for a bit.
Good luck and congrats on your baby.