Why can't men go into the room of a woman who has just given birth?

According to the custom (superstition) in most northern areas, it is unlucky and bad for a woman who has just given birth to a child to live in a room full of flesh and blood. And it's not appropriate for family members to go in. Another custom is to live in someone else's house to give birth, and the host won't let you give birth in it (taboo blood gas).