(IF they didn't get home, which is what Happened in Admiral Janeway's original timeline.)
She could be an Engineer but she couldn't be chief engineer and look after a baby. He could be a Helmsman but he couldn't be chief Helmsman and look after a baby... Something had to give and it could have been the baby.
Sam got through it because Neelix was her boyfriend, and he kept their ship right. Since it's unlikely that either Tom or B'Elanna was going to pay for childcare with sex to someone who wasn't even their anymore, one of them was going to have to go to half duties or no duties.
So who got to stay home with the Kid 24/7?
Tom or B'Elanna?
And what did that mean for the ship?