Contractility of the human uterus recorded by new methods.

Abstract

Rhythmic uterine contractions during pregnancy attributable to rhythmic contractions of smooth muscle have been measured by the pressure exerted on the physiological contents of the uterus (ovum and placenta). During pregnancy and the first and second stages of labor the amniotic fluid pressure is recorded. During the third stage the placental pressure is recorded. A comparison of the different periods during pregnancy shows that a relationship exists between intensity and frequency of contractions and that frequency varies inversely to the square root of the intensity. The absence of definite relationship between the pain and intensity of contractions has been found. Intensity has been found to vary from .5 to 4 cm of water during pregnancy to 35-40 cm of water during the third stage of pregnancy. Frequency of contractions varies from 10 to 30 per 10 minutes during pregnancy to 2-5 during the third stage of labor. Tonus varies from 4 to 11 cm of water during pregnancy to 5-10 cm of water during the third stage. The functions of the first contractions of the third stage of labor are also discussed.