The best time for men to approach women and get a positive response from them may be during the fertile period, when the fair sex seem to lower their guard, a new study has revealed.
To reach the conclusion, researchers selected handsome young men and asked them to experimentally hit on women on a street corner to determine whether fertility affects receptivity to male advances.
"These studies did not focus on women's behaviour. It's the first study to test the role of the menstrual cycle on courtship request, in a real social context and not in laboratory," New Scientist quoted Nicolas Guéguen, a psychologist at the University of South Brittany, France.
To bridge that gap, the researcher asked five handsome 20-year-old men - winnowed down from a larger group rated for attractiveness by 28 women - to ask unsuspecting females for a date.
On sunny summer days, the hunks approached the first young woman they saw on a street corner and delivered a standard pick-up line: "Hello. My name's Antoine. I just wanted to say that I think you're really pretty. I have to go to work this afternoon, and I was wondering if you would give me your phone number. I'll phone you later and we can have a drink together someplace."
If the woman gave their number, "Antoine" then said: "See you soon," and left.
If the women declined, they were given a cheery standard response: "Too bad. It's not my day. Have a nice afternoon!"
Immediately after the encounter, regardless of how the female responded, a female researcher approached the woman and informed her of the study, then asked for her help in completing a short questionnaire.
The survey asked questions about age, contraception use, days since her last period and pregnancy status - none of which were direct measure of her likely disappointment at the deception.
After analyzing responses from 455 women - only 51 declined the survey - Guéguen noticed a couple of trends.
Overall, 8.6 percent of the women who filled out a survey gave out their phone numbers. Rough odds, considering the men were judged as hunks.
Women off the pill accepted offers twice as often as women on the pill (5.8 percent as opposed to 12 percent), perhaps a reflection of the likelihood that women on the pill are more likely to have men in their lives than women not taking birth control.
Among women off the pill, those in their fertile phase accepted 21.7 percent of advances, while women in the midst of their periods gave out their numbers to just 7.8 percent of men, a significant statistical difference that did not exist for women on the pill, the study found.
Hormones may play a role in the study's results. For example, levels of the hormones estradiol (a form of estrogen) and progesterone wax and wane during a woman's cycle, and most oral contraceptives contain progesterone.
However, Guéguen cautions that a woman's relationship status may mask such associations, since single women may be less likely to be taking birth control pills.
The study has been published in the journal Biological Psychology.