What's vital for childbirth without doctor (4)
I believe the answer is:
womb
'what's vital for childbirth' is the definition.
(children grow in wombs)
'without doctor' is the wordplay.
'without' becomes 'wo' (abbreviation of 'without', normally with a slash).
'doctor' becomes 'MB' (Bachelor of Medicine, Medicinae Baccalaureus).
'wo'+'mb'='WOMB'
(Other definitions for womb that I've seen before include "Place of origin" , "Organ in which young develop" , "Organ housing fetus" , "Place of gestation" , "Embryo's home" .)