Listen up, especially if you're thinking of having a child: a UCLA study has shown that women's voices get higher (and more alluringly feminine) as ovulation (and increased fertility) approaches. Researchers recorded the voices of 69 women during high- and low-fertility phases and found that as fecundity climbs, so does pitch. Surprisingly, voice changes occurred only when the women spoke an introductory sentence ("Hi, I'm a student at UCLA") and not when they pronounced vowels. This could suggest that the variation happens just when people are conveying a message, and so it's done, unwittingly, for effect. The research adds to a chorus of studies demonstrating that humans exhibit other cues, such as dressing differently, around ovulation. As for women who are ovulating and don't want to advertise that fact? Try e-mail.