There is no reason to make assumptions about intelligence based on whether a woman does or does not want to have kids. The desire for children comes from a much deeper level and affects women the same regardless of their level of intelligence. It could just as easily be argued that the smarter women are those who recognize their desires and choose to accept them.
I know there was some ridiculous study published stating this a while ago, but there are far more scientists that disagree with the methods than agree wit them. It's a personal choice, but I don't think intelligence has anything to do with it. Many (but not all, or even most) of the women who don't want kids feel that way because they choose to focus on careers instead, and really driven people tend to be more intelligent which could inflate numbers, but I don't think there's any real, legitimate difference in intelligence.