Female Orgasm May Be Tied to 'Rule of Thumb' Sex researchers say 27 percent of women don't climax during vaginal sex.

Sept. 4, 2009 -- First came the G-spot, then multiple climax and spiritual tantric sex. The modern woman is not only expected to be a good mother and a professional success, but some believe she needs to behave like a porn star in the bedroom.

So if a simple device could reveal whether a woman is capable of a vaginal orgasm, would it take the pressure off heterosexual women to perform?

New research suggests that a simple measurement -- a "rule of thumb" -- might be the key to the pleasures of sexual intercourse.

About 75 percent of all women never reach orgasm from intercourse alone -- that is without the extra help of sex toys, hands or tongue. And 10 to 15 percent never climax under any circumstances.

The Internet is rife with non-orgasmic women who say they are missing out, and statistics suggest that they are a significant group.

"Maybe my boyfriend and I aren't doing it right or something," one woman wrote on WebMD.com. "I don't understand. I feel like less of a woman because I can't have an orgasm and I want to so bad. I feel incomplete sometimes after sex."

"I enjoy sex, my partners enjoy the sex," said another on EmpowHER.com. "The guy I'm with right now is frustrated because he's never had a problem making a women happy until now, and it's frustrating for me because I just don't understand."

"What's wrong with me?" asks another on Steadyhealth.com. "I never told anyone this before, but I feel like this is my only option as I am too shy to go to the doctor's."

But it might not be all in their heads, according to Kim Wallen, professor of behavioral neuroendocrinology at Emory University.

He wants to determine if a woman's ability to have an orgasm with penile stimulation alone depends on how far her clitoris lies from her vagina -- the so-called "C-V distance."

Wallen said understanding more about a woman's anatomy might enhance her sex life.

"I suspect that for a large proportion of women, orgasm from intercourse alone is just never going to happen and knowing that might give women some solace."

Female Orgasm Elusive, Say Scientists

Wallen is testing data that was gathered nearly a century ago by the great-grand niece of Napoleon Bonaparte, who suffered from what was then called "frigidity."

Princess Marie Bonaparte, a French psychoanalyst, discovered that the optimal C-V distance is 2.5 centimeters, about an inch, or the space between the fingertip and the thumb.

After collecting data and publishing a report in 1927, her story did not end well. She underwent two experimental surgeries to remedy her own situation, attempting to bring her clitoris closer to her vagina.

She ended up scarred and abandoned finding a physical cure for non-climactic women.

"It was kind of sad," said Wallen. "It's a very interesting metaphoric story. She ended up being a Freudian and totally denied the physical explanation of orgasm. The psychological explanation being if you didn't achieve orgasm it was because you had not grown up."

Despite her travails, he said the data is "highly suggestive, but not demonstrative" that Bonaparte was right.

"Just as there are physical attributes that would prevent some people from ever becoming a concert violinist, or run the 100 meters in 10 seconds, there are attributes that make it unlikely that some women will ever experience orgasm from intercourse alone," he said.

Though what he coined the "rule of thumb" oversimplifies the biological question, it could be a "boon to women."

Four years ago, Wallen set out to do a well-controlled modern study with the collaboration of Elisabeth Lloyd, a professor of history, philosophical science and biology at the Indiana University.

Lloyd's study of 80 years of previous sex research in her 2005 book, "The Case of the Female Orgasm," debunked theories that there is an evolutionary reason for the female orgasm.

She determined the female orgasm is merely a byproduct of the male orgasm, as both sexes share the same genital nerve tissue in the fetal stage.

"It is perfectly normal not to have orgasms and there were lots of women in evolutionary time who had no orgasms and it had no impact on their fertility," said Lloyd.

Current studies bear this out, according to the researchers: 98 percent of men say they "always" reach orgasm during sex, while women are "evenly distributed" between "always and never."

Sexual Pleasure in Women Not Evolutionary

"It's clear the male orgasm is strongly selected and it makes sense," said Wallen. "If they don't reach orgasm, they don't leave offspring."

To look at the question in reverse, women have a strong evolutionary selection for nipples -- without them their babies would die, according to Wallen. However, nipples serve no biological purpose in men.

In analysis of the Bonaparte data, the researchers first had to reframe the question. Instead of asking, "Do you have orgasm during intercourse?" they created a "more explicit survey" asking if manual or oral stimulation had been involved.

After analyzing data from 100 female volunteers, ranging from 18 to 60, they found about 11 percent said they always have orgasm during intercourse and the same number said they never climaxed.

Because these surveys were anonymous, Wallen and Lloyd will now re-administer the questions to a new group of women. Ultimately, they hope to design a device that women can use in the privacy of their homes to measure their C-V distance.

Wallen said that if men and women knew the reality of their biology, their sex might improve.

"What is startling and surprising to me is that both men and women buy into the same sort of cultural model," he said. "If he is a good lover, he can bring me to orgasm with his penis alone. And a man buys into that and doesn't offer any kind of stimulation. And because he's not any good, she won't say anything because it's emasculating."

But Susie Bright, a feminist and sex columnist for Jezebel.com, said such studies on the "anomalies" of the female genitalia are "foolish."

"We need to know how to talk about sex and communicate about what feels good and not be so scared," she told ABCNews.com. "It would be helpful if women knew as much about their 'clits' as men do about their penises."

She said that, particularly in young people, misinformation and religious shame prevent many women from enjoying sex. Bright is also critical of abstinence programs and cuts in science classes.

"We should speak to the greater issues, even if there is some validity to this observation," she said. "It's such a miniscule part of womanhood and it's missing the boat."

"I know there's a lot of interest in the female genitals, but that does not get at women's orgasmic possibilities," said Bright. "Knowing that they are different, they will say, 'Oh my God, what is wrong with my vulva?"

Study scientist Lloyd agrees that too much emphasis is placed on models of female sexuality that are created by Hollywood and the pornography industry.

But efforts to change attitudes and tell women "just to relax," alone may not help them to achieve orgasm.

"Those things are worthwhile," she said. "But to sort of act as if that's all that needs to be done for women is just silly. This is a total denial of the facts."