The uterine peristaltic pump. Normal and impeded sperm transport within the female genital tract.

Rapid as well as sustained sperm transport from the cervical canal to the isthmical part of the fallopian tube is provided by cervico-fundal uterine peristaltic contractions that can be visualized by vaginal sonography. The peristaltic contractions increase in frequency and presumably also in intensity as the proliferative phase progresses. As shown by placement of labeled albumin macrospheres of sperm size at the external cervical os and serial hysterosalpingoscintigraphy (HSSG) sperm reach, following their vaginal deposition, the uterine cavity within minutes. In the early follicular phase a large proportion of the macrospheres remains at the site of application, while a smaller proportion enters the uterine cavity with even a smaller one reaching the isthmical part of the tubes. In the mid-follicular phase of the cycle with increased frequency and intensity of the uterine contractions the proportion of macrospheres entering the uterine cavity as well as the tubes has significantly increased. In the late follicular phase with maximum frequency and intensity of uterine peristalsis the proportion of macrospheres entering the tube increases further at the expense of those at the site of application as well as within the uterine cavity. The transport of the macrospheres into the tube is preferentially directed into the tube ipsilateral to the dominant follicle, which becomes apparent in the mid-follicular phase as soon as a dominant follicle can be identified by ultrasound. Since the macrosphere are inert particles the directed sperm transport into the tube ipsilateral to the dominant follicle is not functionally related to a mechanism such as chemotaxis but is rather provided by uterine contraction of which the direction may be controlled by a specific myometrial architecture in combination with an asymmetric distribution of myometrial oestradiol receptors. Women with infertility and mostly mild endometriosis display on VSUP a uterine hyperperistalsis with nearly double the frequency of contractions during the early and mid- as well as midluteal phase in comparison to the fertile and healthy controls. During midcycle these women display a considerable uterine dysperistalsis in that the normally long and regular cervico-fundal contractions during this phase of the cycle have become more or less undirected and convulsive in character. Hyperperistalsis results in the transport of inert particles from the cervix into the tubes within minutes already during the early follicular phase, and may therefore constitute the mechanical cause for the development of endometriosis in that it transports detached endometrial cells and tissue fragments via the tubes into the peritoneal cavity. Moreover, dysperistalsis may contribute to the infertility in these patients since it results in a break down of sperm transport within the female genital tract.