due to age and/or physical health. To me it sounds as though Mrs Norris was still considered young enough to become pregnant when she married, but that Mr Norris's health could have precluded him being able to have a sexual relationship with his wife by the time the story opens. He also sounds as though, because of illness, that he doesn't have the patience or temperment to be a parent, so, just guessing here, perhaps his idea of a marital relationship was more that of patient and nurse and Mrs Norris may have had no choice but to go along with that. If you are foregoing children for financial reasons, why would you care how many children a sibling had?