"Get up the duff" is an informal slang phrase that refers to a woman becoming pregnant. While this phrase may be commonly heard in certain circles, it is important to note that it can be considered offensive or inappropriate in many contexts. There are many more appropriate and respectful ways to discuss pregnancy, such as using terms like "expecting," "pregnant," or "with child." Other slang synonyms for "get up the duff" include phrases like "in the pudding club," "bun in the oven," or "up the sprout." Ultimately, it is important to consider your audience and choose language that is both respectful and accurate when discussing pregnancy.