Midwife essentially is to assist to give birth (5)
I believe the answer is:
whelp
'give birth' is the definition.
(thesaurus)
'midwife essentially is to assist' is the wordplay.
'essentially' indicates the central letters.
'is to assist' becomes 'help' (I've seen this before).
The centre of 'midwife' is 'w'.
'w'+'help'='WHELP'
'to' acts as a link.
(Other definitions for whelp that I've seen before include "impudent young lad" , "Have puppies" , "Give birth to (a puppy)" , "Produce issue" , "Young mammal" .)