up the duff

Definition

Slang

  • adjective pregnant. A working-class synonym of up the poke/pole/spout/stick, here employing the long-established British metaphor of pudding. duff is an old-fashioned boiled or steamed pudding; the word is a dialect version of ‘dough’. It has an all-purpose sexual sense (encompassing gratification, the penis, semen or a woman and baby).
http://www.dictionarycentral.com/definition/up-the-duff.html