For instance Kratochvíl (1994) surveyed 200 women and found that 6% reported ejaculating, an additional 13% had some experience and about 60% reported release of fluid without actual ejaculation. Reports on the volume of fluid expelled vary considerably from amounts that would be imperceptible to a woman, to mean values of 1–5 ml, although much higher volumes have been reported.
Much of the problem in arriving at a consensus relates to a failure to adopt generally agreed-on definitions and to research methodology. Research on this subject has used highly selected individuals, case studies, or very small numbers of subjects, making generalisation difficult, hence the continuing controversies and debates. For instance, much of the research into the nature of the fluid concentrates on trying to determine whether it is urine or not. Problems relate to the difficulties involved in the collection of specimens and of contamination. Since the area of interest is para-urethral glands, it is impossible to completely separate the secretions from urine, especially where there may be retrograde ejaculation back up the urethra towards the bladder. The best data comes from studies where women have abstained from coitus, and where their own urine is used as controls, pre and post orgasm. One way of sorting this out is the use of chemicals that are excreted in the urine, so that any urinary contamination can be detected. Another methodological issue arises from the fact that the composition of the fluid appears to vary with the menstrual cycle, while the biochemical profile of the para-urethral tissues also varies with age. Other issues relate to the sensitivity and specificity of the markers chosen. The key questions are the source of the fluid produced, and its nature. Some findings have been presented in conferences but never published in peer review journals, and many others are in difficult to access resources.
Relation to urinary incontinence
For most of the last century, there was controversy over whether the effect existed at all, and in recent history there has been confusion between female ejaculation and urinary incontinence. Even in 1982, Bohlen explained the accepted wisdom;
The previously accepted notion that all fluid expelled during a woman's orgasm is urine is now being challenged...sexologists must take care not to assume now that any fluid produced at orgasm is "female ejaculate".
However, scientific studies from the 1980s and later have demonstrated that a substance is produced which is distinct from urine, though it shares some qualities, such as alkalinity, with urine. But women claiming to have ejaculations who have agreed to urethral catheterization prior to intercourse expelled large volumes of urine through the catheter at orgasm. There is no doubt that some women are frankly incontinent of urine at orgasm (coital incontinence), which can be distressing. A recent study of women who claim to ejaculate found no evidence of any urological problems, suggesting these two conditions (ejaculation and coital incontinence) are quite distinct physiologically, although perhaps not always distinguishable in a particular woman's mind. For instance Davidson's study of 1,289 women found that the sensation of ejaculation was very similar to that of urination. It may be important to sort out whether there is in fact any incontinence in women who present complaining of this, to avoid unnecessary interventions. It is important to distinguish orgasmic ejaculation from vaginal discharges which may require investigation and treatment. However in individual cases, the exact source of any reported discharge may not be obvious without further investigation.
Nature of fluid
Critics of the concept have maintained that ejaculation is merely either stress incontinence or vaginal lubrication. Research in this area has concentrated almost exclusively on attempts to prove that it is not urine measuring substances such as urea, creatinine, prostatic acid phosphatase (PAP), prostate specific antigen (PSA), glucose and fructose levels. Early work was contradictory, for instance the initial study on one woman by Addiego and colleagues reported in 1981, could not be confirmed in a subsequent study on 11 women in 1983, but were confirmed in another 7 women in 1984. But in 1985 a different group studied 27 women, and found only urine, suggesting that results depend critically on the methods used.
A 2007 study on two women, involved ultrasound, endoscopic and biochemical analysis of fluid. The ejaculate was compared to pre-orgasmic urine from the same woman, and also to published data on male ejaculate. In both women, higher levels of PSA, PAP, glucose but lower levels of creatinine were found in the ejaculate. PSA levels were comparable to those in males.
Source of fluid
One very practical objection relates to the claims about the volume ejaculated, since this has to come from some storage area in the pelvis, of which the urinary bladder is obviously the largest source. The actual volume of the para-urethral tissue is quite small. By comparison, male ejaculate varies from 0.2–6.6 mL (0.04–1.3 tsp) (95% confidence interval), with a maximum of 13 mL (2.6 tsp). Therefore claims of larger amounts of ejaculate are likely to contain at least some amount of urine. The eleven specimens analyzed by Goldberg in 1983, ranged from 3–15 mL (0.6–3.0 tsp). One source states that Skene's glands are capable of excreting 30–50 mL (6–10 tsp) in 30–50 seconds. but it is unclear how this was measured and has not been confirmed. One approach is to use a chemical like methylene blue (or drugs like Urised which contain it) so that any urinary contamination can be detected. Belzer showed that in a woman he studied, the dye was in her urine, but not her orgasmic expulsion.
PAP and PSA have been identified in the para-urethral tissues, using biochemical and immunohistochemical methods, confirming that the ejaculate likely arises from the ducts in these tissues, in a manner homologous to that in the male. Another marker common to the prostate tissue in both male and female is Human Protein 1.
However, studies on the actual penis are very limited compared to those on the tissues of likely origin. PSA occurs in urine, which is elevated in post-orgasmic samples, compared to pre-orgasmic. Simultaneous collection of ejaculate also showed PSA in all cases, but in higher concentration than the urine.
