Expecting initially positive ruling (8)
I believe the answer is:
'expecting' is the definition.
'initially positive ruling' is the wordplay.
'initially' says to take the initial letters.
'ruling' becomes 'regnant' ('regnant' can be a synonym of 'ruling').
The initial letter of 'positive' is 'p'.
(Other definitions for pregnant that I've seen before include "loaded" , "Gravid" , "Expecting a baby" , "Expecting a child" , "With child, enceinte" .)