Spinnbarkeit: a characteristic of cervical mucus; significance at ovulation time

Accurate timing of ovulation is especially necessary (1) in artificial insemination in order to avoid wastage of donor semen; (2) in cases where the husband is relatively infertile and it is necessary to conserve his semen. While many physicians rely upon the basal body temperature curve for timing ovulation, the interpretation of such curves is varied. Some physicians believe ovulation occurs prior to the lowest point in the temperature cycle, while others believe that ovulation occurs either at the low point or following the thermal shift. We have been disappointed in our ability to interpret the basal body temperature curve for accurate timing of ovulation, and have placed greater reliance upon concurrent phenomena, such as changes in the quantity and viscosity of cervical mucus and the cyclic changes observed in the vaginal smear. Although the relationship between the occurrence of a profuse, thin cervical mucus discharge and the optimal time of fertility in the human has been recognized for the past century, in our opinion this relationship requires further evaluation. In his excellent review, "Cervical mucus: Cyclic variations and their clinical significance," Shettles quotes Robin who, in 1848, noted the viscous nature of human cervical secretions; and Smith who, in 1865, concluded that conception is most likely when the mucus contents of the cervix are in the most fluid condition. J. Marion Sims, who invented a vaginal speculum and first described the postcoital examination in 1868, observed that the test is positive for motile spermatozoa when the cervical mucus becomes clear and translucent, and about the consistency of the white of egg. Although these observations on human cervical mucus have been well documented, they have been almost disregarded by gynecologists. The significance of the cyclical outpouring of cervical mucus has been rediscovered in the past few years and has aroused great interest in students of sterility. The optimal time of fertility in domestic animals is the period of heat or estrus. In 1925, Woodman and Hammond showed that during estrus, bovine cervical mucus is fluid and capable of being drawn out into threads, whereas in diestrus the mucus is thick. Seguy and Vimeux, and Seguy and Simonnet called attention to the optimal conditions of longevity of human spermatozoa in the fluid, glairy mucus of the cervix at midcycle. They postulated that these changes in cervical mucus were associated with ovulation and could be compared to the period of estrus in subprimate mammals. They correlated these changes with visual evidence of ovulation at laparotomy. Subjectively, many women observe an increased sticky, mucoid discharge which is typical at midcycle and which is present over a period of days. On occasion this discharge is blood-tinged and may be compared to the distinct bloody mucoid discharge present in the domestic animal "in heat." This mucus can be seen exuding from the cervix at midcycle and it may be aspirated from the endocervix and actually weighed, as reported by Viergiver and Pommerenke. Clift demonstrated certain rheologic properties of cervical mucus, especially flow elasticity and Spinnbarkeit. Flow elasticity, or elastic recoil of mucus, is measured by an instrument described by Blair. The use of the Blair capillary viscometer is a cumbersome method which we discontinued. We have had no experience with the new modification of the viscometer described by Clift, Glover, and Blair. Spinnbarkeit is easily tested, and we have found it to be a very practical objective method for determining viscosity of cervical mucus. In performing this test (Fig. 1), a vaginal speculum is inserted, exposing the cervix. A glass cannula is inserted into the endocervix and by means of gentle suction, a quantity of endocervical mucus is obtained. This mucus is blown onto a glass slide and a cover slip is placed on it. The mucus adheres to both the slide and the cover slip, and by withdrawing the cover slip, a thread of mucus is formed which can be measured in centimeters (Fig. 2). Usually, the cover slip is withdrawn several times, and the average length of the thread is ascertained. It is our purpose to show the relationship of Spinnbarkeit to other cyclic phenomena occurring during the menstrual cycle, such as basal body temperatures, vaginal smears, quantity of cervical mucus, and longevity of spermatozoa (Fig. 3).