Doctor gets third baby a cot though it's crowded (6)
I believe the answer is:
mobbed
'it's crowded' is the definition.
(mobbing is a kind of crowding)
'doctor gets third baby a cot' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'gets' says to put letters next to each other.
'third baby' becomes 'b' (3rd letter of 'baby').
'a cot' becomes 'bed' (cot is a type of bed).
'mo'+'b'+'bed'='MOBBED'
'though' is the link.
(Other definitions for mobbed that I've seen before include "Fell on" , "Oppressed by crowd" , "Crowded round (someone) in disorderly manner" , "Surrounded in acclaim" , "Attacked by angry or enthusiastic crowd" .)