Why do women believe they are medical experts on the human body because they've had babies?

I was reading a question about during birth/labor and one lady said that you cannot put anything up there after the water has broken, but that just isn't true. She then went on to say that she knew this because she was the mother of a 6 month old child and had given birth before. Wouldn't this logic be comparable to say, knowing how the brain works because you use it everyday? Or knowing how a car works because you can operate the controls? I find many women have this sort of mentality that just because they have experienced one little facet of something they are automatically some sort of expert on everything about that something.