The uterus, the organ responsible for nurturing new life, undergoes a series of significant changes during sexual response. In ancient medicine, it was referred to as the baogong (womb) or female womb. Shaped like an inverted pear that is slightly flattened anteroposteriorly, the uterus in adult women measures approximately 7–8 cm in length, 4–5 cm in width at the fundus, and 2–3 cm in thickness, weighing roughly 40–50 grams. It is anatomically divided into three parts: the fundus, body, and cervix. The fundus and body are demarcated by the entry points of the fallopian tubes; the rounded upper portion is the fundus, and the region below is the body. The tapered segment extending from the body to the distal end is the uterine cervix, approximately 2.5–3 cm long and roughly cylindrical. Its lower third protrudes into the vagina and is known as the vaginal portion, while the upper two-thirds lie within the pelvic cavity. The central opening at the distal end of the cervix is the external os, which connects the uterus to the vagina. In nulliparous women, it is smooth and oval; in parous women, childbirth transforms it into a transverse slit, dividing the cervical os into anterior and posterior lips. The uterine wall is primarily composed of smooth muscle, with the thickest myometrium in the upper segment of the uterine body. After childbirth, the uterine weight may double, and the organ gradually atrophies and shrinks following menopause.
We consider the uterus as an integrated structure and examine its changes during sexual response as a whole.
I. Uterine Elevation Response
As sexual tension progresses from the excitement phase to the plateau phase, the entire uterus ascends from the lesser pelvis into the greater pelvis. Under normal conditions, the cervix lies in contact with the posterior vaginal wall; during arousal, it slowly shifts posteriorly and superiorly, creating an anatomically oval, concave space between the cervix and the anterior/posterior vaginal walls. Resembling a raised tent, this response is often called the tenting effect. The lower portion of this space is also referred to as the seminal receptacle, where semen accumulates shortly after ejaculation. Uterine elevation is completed by the end of the plateau phase, and the uterus returns to its original position in the lesser pelvis during the resolution phase. The cervix naturally descends, with the external os immersing into the seminal pool.
Supportive tissues of the uterus are believed to play a critical role in this elevation response. Damage to supportive structures such as the cardinal ligaments and uterosacral folds from childbirth trauma significantly slows or weakens uterine elevation. Marked congestion of pelvic organs, including the broad ligaments, due to sexual tension also contributes to uterine elevation: venous engorgement shortens and tightens these structures, secondarily lifting the uterus. Notably, a retroverted uterus does not exhibit this elevation response during sexual activity.
II. Cervical Response
Contrary to previous assumptions, the cervix does not secrete fluids during sexual response as previously thought. Only in the late plateau phase, after the vaginal walls have become fully lubricated, does the cervix release a small amount of ovulatory-type mucus—thin, clear, and highly elastic.
A distinctive cervical reaction occurs specifically during the resolution phase following orgasm: the external cervical os dilates slightly. This physiological change is not observed in women who do not achieve orgasm. The os remains open for approximately 20–30 minutes before closing, most prominently in nulliparous women. In parous women with significant obstetric trauma, this dilation cannot be reliably identified. Theoretically, cervical dilation during resolution increases the chance of sperm entering the uterine cavity; however, many women conceive repeatedly without ever experiencing orgasm.
III. Uterine Body Response
The classic response of the uterine body during orgasm is rhythmic myometrial contractions. These originate at the fundus, propagate through the body, and end in the lower uterine segment. Similar to early labor contractions, they are characterized by smaller amplitude but higher frequency. Such contractions typically begin 2–4 seconds after the woman subjectively perceives the onset of orgasm, with intensity correlating directly with her subjective experience.
It is widely recognized that uterine contractions during orgasm induced by masturbation are more intense and longer-lasting than those during penile-vaginal intercourse, consistent with women’s subjective reports. Confirmed uterine contractions during orgasm help explain the cramping discomfort some women experience at climax, particularly postmenopausal women, who often report pain from these contractions.
Prior to the experimental research of Masters and Johnson, the cause of genital pain in women after prolonged or continuous sexual arousal was unknown. Their work revealed that this discomfort stems from severe, unresolved vascular congestion of pelvic organs, resulting in pain and pressure—pathophysiologically similar to chronic pelvic venous congestion, though more acute. Due to this vascular engorgement, uterine volume may increase by 50–100% during the plateau phase, with congestion worsening the longer stimulation continues. After orgasmic release, uterine swelling subsides within 10 minutes in nulliparous women and within 10–20 minutes in parous women. If orgasm is not achieved, uterine involution takes 30–60 minutes. The enlargement of the uterus during sexual response further confirms deep tissue congestion in target organs. Like other structures (the outer third of the vagina forming the orgasmic platform, labia minora, and breasts), the uterus responds to effective sexual stimulation with vascular congestion and fluid accumulation, leading to increased organ volume.
Masters and Johnson observed that when menstruating women achieved orgasm via masturbation, menstrual blood was forcefully ejected from the external cervical os at the moment of orgasm or during the initial seconds of resolution. In many cases, pressure was sufficient to propel blood straight out of the vagina without touching the blades of a speculum placed inside. Since the speculum elevates the cervix away from the vaginal opening, this phenomenon was clearly visible, demonstrating that uterine contractions are quite powerful and not spasmodic.