What did his wife have to do when she was pregnant?

I think Jesse Bentley made his preagnant wife work as hard as all the other women had to do on the farm. After she gave birth, she died. Check this quote out:

"As a matter of fact, Jesse's wife did soon go under. That was perhaps Jesse's fault. A farm in Northern Ohio in the hard years after the Civil War was no place for a delicate woman, and Katherine Bentley was delicate. Jesse was hard with her as he was with everybody about him in those days. She tried to do such work as all the neighbor women about her did and he let her go on without interference. She helped to do the milking and did part of the housework; she made the beds for the men and prepared their food. For a year she worked every day from sunrise until late at night and then after giving birth to a child she died."

This quote was from a very informative site on this novel. I'll include it in the source link below.