All the really smart, well educated women I know (I’m talking very high up Barristers, Solicitors, Consultants etc) either have no children or one and had them much later (early 40’s).
I think this is complicated by the fact that it cuts both ways, so women who have a lot of children may find it harder to progress, despite being as intelligent as the very senior ones. If I think about the women I was at college with, it's true that the ones with the senior jobs tend to have two or fewer children, but they weren't necessarily the most intelligent ones.
Im not sure if anyone has ever compared career progression (take earnings as a proxy) vs IQ for men and women. I'd bet that there is a greater correlation for men than for women.