Up the pole
Being “up the pole” has carried a wide range of meanings in different times and places. But many sources associate the meaning “pregnant” with the phrase as used in Ireland, and the context supports that reading. UrbanDictionary.com says, "Pregnant, usually unplanned, Irish slang, as in 'knocked up.'"
A pregnant girlfriend would explain Seymour’s sudden decision to abandon his study of medicine and secure one of the few near-certain sources of gainful employment available to young men in 1904 Dublin.