Quaker colonist, regularly pregnant (4)
I believe the answer is:
penn
'quaker colonist' is the definition.
(I've seen this in another clue)
'regularly pregnant' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'pregnant' are 'PENN'.
(Other definitions for penn that I've seen before include "founder of colony" , "Early Quaker leader" , "Milk actor" , "Colonising Quaker" , "William --, founder of a US state" .)