That's wrong. The most important reasons for declining birthrates are, tataaa!!!: Growing wealth and better education (especially of women) Feminism is playing a part too, but not in the way you are implying.
Look at scandinavian countries, or France, where equality and chances for women are amongst the best in the western world (and one could pretty safely assume that this is due to liberal feminism): They have also the highest birthrates.
Of course you could try and turn back time to that ooooh soooo glorious times when women where just working slaves and birth machines. However, i think (and hope) you would be pretty much alone.
Btw, i never heard of liberal feminism in classic Rome or Greece, but i could be mistaken.