Powder used in post-natal care (4)
I believe the answer is:
talc
'powder' is the definition.
(I know that talc is a kind of powder)
'in post-natal care' is the wordplay.
'in' indicates a hidden word.
'TALC' is hidden within 'post natal care'.
'used' is the link.
(Other definitions for talc that I've seen before include "Bathroom powder (abbr)" , "Soft white powder" , "Powder used as toiletry" , "Powdered substance" , "Cosmetic powder" .)