how does a 27yearold female loose intrest in sex?

You are answering your own question right there, she gave birth. She had a child, that means she has more stress and worries in her life. I have to wonder if it affects yours at all. So one she is probably tired constantly, two, she might not feel as attractive as she used to either. What you need to do is make sure she feels beautiful and appreciated, help her out in things. Do little things for her, tell her you love her. Hug her and kiss her out of the blue. Make her feel loved. And if that doesn't work, remember she is raising a child now, she will be tired and more concerned with the baby, it happens. Just make sure to let her know, that is is loved, she is still beautiful and sexy to you also. And perhaps every so often, take a night and go out just the two of you enjoy yourselves without worrying about the baby. Let the baby be with someone you trust.