'Up the duff' is a euphemism for pregnant.

up on something, be. up on (something) up on someone’s bumper. up on (one's) ear. Up the duff is a great week-by- week companion book to read during pregnancy. First published in 1999, Kaz Cooke’s best-selling Up the Duff is firmly established as the most loved and trusted book for Australian and New Zealand women on pregnancy. Up the duffunknown 1. It contains all the most relevant information from babys development, how your body changes with pregnancy, practical tips about what to buy for baby, what to eat, information about medical examinations and doctors visits and contact details for institutions that offer help with everything pregnancy and baby related. up one’s alley. up one's alley. up one side and down the other. What's the origin of the phrase 'Up the duff'? “Well, when he found out that my gran was up the duff, he went back to his native Norway (or it might have been Sweden) [ … 1999, Irvine Welsh, Filth, page 191, It just means that some daft wee hairy that gets knocked up the duff has tae get oan the bus tae Carlisle tae get cleaned oot. up on (one's) bumper. It is used most commonly, although not exclusively, to describe unplanned pregnancy. This 20th-anniversary edition has been fully revised and updated. The slang term for being pregnant 2. up one's sleeve, to have something. 'Up the duff' doesn't appear in print until 1941, in Sydney John Baker's Dictionary of Australian Slang :

A drinking toast with Duff beer in the Simpsons