Female sexual arousal: genital anatomy and orgasm in intercourse

Abstract

In men and women sexual arousal culminates in orgasm, with female orgasm solely from sexual intercourse often regarded as a unique feature of human sexuality. However, orgasm from sexual intercourse occurs more reliably in men than in women, likely reflecting the different types of physical stimulation men and women require for orgasm. In men, orgasms are under strong selective pressure as orgasms are coupled with ejaculation and thus contribute to male reproductive success. By contrast, women's orgasms in intercourse are highly variable and are under little selective pressure as they are not a reproductive necessity. The proximal mechanisms producing variability in women's orgasms are little understood. In 1924 Marie Bonaparte proposed that a shorter distance between a woman's clitoris and her urethral meatus (CUMD) increased her likelihood of experiencing orgasm in intercourse. She based this on her published data that were never statistically analyzed. In 1940 Landis and colleagues published similar data suggesting the same relationship, but these data too were never fully analyzed. We analyzed raw data from these two studies and found that both demonstrate a strong inverse relationship between CUMD and orgasm during intercourse. Unresolved is whether this increased likelihood of orgasm with shorter CUMD reflects increased penile-clitoral contact during sexual intercourse or increased penile stimulation of internal aspects of the clitoris. CUMD likely reflects prenatal androgen exposure, with higher androgen levels producing larger distances. Thus these results suggest that women exposed to lower levels of prenatal androgens are more likely to experience orgasm during sexual intercourse.

Figure 1

Illustrates the sex difference in the occurrence of orgasm in males and females in relation to age. Males show a rapid transition from few boys experiencing orgasm prior to puberty to all men experiencing orgasm soon after puberty. Women, by contrast show a much more gradual developmental curve. Male data are adapted from Kinsey, Pomeroy, and Martin, 1948 and the female data are adapted from Kinsey, et al., 1953.

Figure 2

Illustrates the measurements used to determine the clitoral-urinary meatus distance (CUMD) in a sample of adult women. C, C′, and C″ are the location of the clitoris, M is the location of the urinary meatus, p.l. are the labia minora (petites lèvres in french), F is the fourchette of the vagina, and a,b is the arch of the symphysis pubis. Bonaparte's CUMD measure was from the frenulum of the clitoris (underside of the clitoral glans) to the center of the urinary meatus (Adapted from Narjani, 1924).

Figure 3

The distribution of CUMD measures in the Bonaparte (Narjani, 1924) and Landis (Landis, Landis, and Bowles, 1940) samples. The Bonaparte sample (N=43) had significantly shorter CUMDs than did the Landis sample (N=35) possibly reflecting a difference in the clitoral measuring point used in the two studies.

Figure 4

Average CUMD measurements in the Bonaparte and Landis samples for those women routinely experiencing orgasm in intercourse (orgasm 66% of the time or more) and those not, or experiencing orgasm in intercourse less than 67% of the time (Landis sample). Data are shown for the samples combined and for the CUMD measurements of women in the Bonaparte sample experiencing autosexual orgasms. For the Bonaparte, Landis and Combined samples the differences are statistically significant, although the magnitude of the difference is substantially greater in the Bonaparte than the Landis sample. The difference in CUMD for the autosexual sample is not statistically significant.

Figure 5

Receiver Operating Characteristic curves (ROC) for the relationship between CUMD and orgasm in intercourse for the Bonaparte (5a) and Landis samples (5b). Although both ROCs accounted for significant area under the curve, the Bonaparte sample accounted for more area than did the Landis sample and showed greater sensitivity and specificity. The dashed diagonal like represents 0.5 area under the curve, which would reflect a chance relationship between CUMD and orgasm in intercourse.