Gas in any way curtailed about newborns (8)
I believe the answer is:
neonatal
'about newborns' is the definition.
(I know this)
'gas in any way curtailed' is the wordplay.
'gas' becomes 'neon' (neon is a gas).
'in any way' becomes 'at all' (synonyms).
'curtailed' means to remove the last letter.
'atall' with its final letter taken off is 'atal'.
'neon'+'atal'='NEONATAL'
(Other definitions for neonatal that I've seen before include "Relating to newborns" , "at a very young age" , "Of a new-born infant" , "Relating to the first month of life" , "Relating to the newborn" .)