Canadian researchers found that during ovulation the female genitalia is more responsive to images of penetration than to images of oral sex. The difference is significantly reduced during non-fertile phases of the menstrual cycle.

Vaginal photoplethysmograph used to measure women's genital response at the Sexual Psychophysiology Lab of the Kinsey Institute (credit: Pere Estupinyà)

A couple's preferences and behavior and female reception toward sex changes during the menstrual cycle. Various studies have verified that during the ovulation period women experience higher levels of sexual desire and fantasies, masturbate more, dress in more seductive clothing, prefer men with more clearly defined masculine traits, enjoy sex more, and reach orgasm more easily, and for bisexual women their desire for men, instead of women, is more pronounced.

Something that had not yet been established within this variability was whether women have more of an inclination for a certain type of sexual practice over another according to the moment in her menstrual cycle that she finds herself in.

To verify this, Kelly Suschinsky from Meredith Chivers' Sexuality and Gender Laboratory at Queen's University in Canada conducted the following experiment: She selected a group of heterosexual women between the ages of 18 and 40, all of whom had normal menstrual cycles, were not taking prescription drugs, and had abstained from sex for at least 24 hours, and showed them various erotic films with images of penetration and oral sex. She conducted the same experiment twice during ovulation and days later during the luteal phase (non-fertile).

While the women observed the different films, researchers measured the women's genital arousal with a vaginal photoplethysmograph. They were also asked about the level of subjective excitement that they experienced. The images, which had already been used in previous experiments, had proven to be arousing for the majority of women. In order to avoid any distortion in the information according to the order in which it was shown, half of the group started with images during their ovulation phase and the other half started with images during the luteal phase.

The results were highly significant: When the films were shown for the first time during ovulation, the genital response was fives times greater while observing penetrative than it was while observing oral sex. In contrast, when they were shown during the luteal phase, images of both penetration and oral sex generated a very similar response to each other. It was clear that the women's vaginas during ovulation reacted more intensely to images of penetration than they did during more non-fertile phases of the menstrual cycle.

The Mind and Genitalia Aren't Always Well-Connected

Curiously, the statements offered by volunteers regarding their subjective perception of arousal did not vary as much. This corresponds with the results from a previous group tested by Meredith Chivers, a pioneer in research on sexual concordance of mind and genitalia. Chivers has demonstrated that physical stimulation of the clitoris and vagina does not always coincide with any mental stimulation experienced by women on a subjective level. There are images or sexual situations that, for various reasons, do not prove mentally stimulating or are, in fact, not liked but still generate an unconscious and uncontrollable response of excitement in their genitalia.

The First Sexual Encounter Could Condition the Rest

Another interesting result of the experiment showed that the testing order mattered and could establish certain preferences in the long run: The women who were shown the first set of films during ovulation showed a clear preference for penetration over oral sex, which diminished but remained during the luteal phase. Those who began in their non-fertile phase, in contrast, generated similar stimulation in response to images of both oral and penetrative sex, while after ovulation their preference for penetration grew considerably but without ever reaching the differences observed in the women who had begun during ovulation.

In the article's conclusions, researchers speculate that a woman's menstrual cycle can influence a couple's sexual practices during their first sexual encounter, and that this can slightly condition preferences and levels of satisfaction later on.

Clearly, the menstrual cycle isn't the only factor intervening in a woman's complex sexual behavioral response. But except for bonobos and humans, female mammals only experience excitement during ovulation, and it would make sense that this internal programming still exerts a certain unconscious influence in the sexual behavior of women today.

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