"The only time in the cycle when estradiol levels are high and progesterone levels are simultaneously low is the late follicular phase, near ovulation when fertility is highest," said the study's lead author David Puts, an assistant professor of anthropology at Pennsylvania State University.
A group of more than 500 women were also asked to rate women's attractiveness across their cycles.
They scored the photographs and vocal recordings based on two measures: flirtatiousness and attractiveness to men. Women rated the subjects higher on both measures when the subjects were in their more fertile phase.
