The province of maternity (5)
I believe the answer is:
natal
'the province' is the definition.
(I have seen 'old province' mean 'natal' so perhaps 'province' could also mean 'natal')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for natal that I've seen before include "dealing with delivery" , "of an ass?" , "To do with birth - in S Africa?" , "Like a birthday" , "Relating to birth - former South African province" .)