There is a fertility modifier for those ancilliaries.

for example:
Ancillary wise_woman
Image older_woman_ancillary.tga
ExcludedAncillaries herbalist, doctor, chirugeon
ExcludeCultures carthaginian, eastern, egyptian, greek, roman
Description wise_woman_desc
EffectsDescription wise_woman_effects_desc
Effect Fertility 1
Effect BattleSurgery 10