Don't have custody of their children.
If I hear about a woman who doesn't have custody of her children, I always wonder why? There is nothing in this world that could make me give up my children, nor would I ever allow myself to be in a position to lose them. You are their mother, you are supposed to be the most stable part of their life (you, and their father). I am not talking about shared custody with a father. I completely understand and greatly respect that. I am talking about the mothers whose child lives with their parents, or lives with the father full time, etc. Those kinds of situations just don't make sense to me.
I'm sure there are going to be people who have a fit and tell me that I don't know these people's situations. And they will be right, I don't. But I cannot picture a situation that for me it would be acceptable to give up my children. To me, a mother always finds a way.