Continuous measurement by radio-telemetry of vaginal pH during human coitus.

Abstract

Summary. The use of the pH-pill has allowed continuous monitoring of vaginal pH during human coitus. In the case of a couple of normal fertility, there was an immediate buffering by seminal plasma so that the vaginal pH changed in 8 sec from pH 4·3 to pH 7·2. In the case of a couple of low (male) fertility, the immediate effect of the arrival of semen in the vagina was a change from pH 3·5 to pH 5·5. A similarly small change in pH occurred when the seminal volume of a fertile male subject had been depleted, by repeated ejaculation, to 1 ·5 ml. At this pH (5·5), spermatozoa are generally immobilized. It has been possible to alter normal fertility, as judged by postcoital tests for sperm motility, by the introduction of a pH 3·6 buffer solution into the vagina before coitus. In this latter experiment, the vaginal pH immediately after ejaculation was 5·0 and, after 2 hr, had reached pH 5·4. These results in vivo suggest that the vagina is not the hostile environment hitherto imagined, since the normal ejaculate readily overcomes the vaginal acidity by its powerful buffering action. Low seminal volume, with or without a concomitantly low sperm count, and artificial changes in vaginal environment by buffer solutions may affect fertility.