I'd probably call them "Maternity Hospitals". With a "Maternity Index", functioning in a similar way to the current health index. Each Maternity Hospital above the needed number, would have a diminishing rate of return. With high Maternity Indexes giving a boost to the birth rate.
Alternately, a far easier way to implement it. Would be to have the existing Health Index, also provide a boost to the Birth Rate.
This would be a method for successful players to boost their population soft cap, through playing well. I'd be interested to hear what people have to say about it?
Signed President of DanNation on LU