The contractions of the human uterus during pregnancy and labor

Abstract

R ECENT studies of the motility of the nongravid human uterus have revealed the presence of a cycle of myometrial activity under the control of the ovarian hormones.1-3 The contractions in the follicular phase of the menstrual cycle are characterized by small amplitude, short duration, short intervals between contractions, and high tonus. In the luteal phase, which follows ovulation, the contractions gradua.lly increase in amplitude and duration but decrease in frequency and tonus. The maximum amplitude is reached as a rule at the onset of menstruation after which there is a gradual return of the small waves. This cycle has been reproduced in castrates by administering the ovarian hormones in the natural sequence: first estrogen alone and then together with progesterone.4 The possibility that the change from the follicular to the luteal phase contractions represents a prograwid phenomenon, analogous to the secretory transformation of the endometrium, stimulated this study of the motor activity of the uterus during pregnancy and labor, which was begun in October, 1939. The misconception has arisen in some quarters that the uterus, under the alleged inhibitory influence of progesterone, remains quiescent during pregnancy. While this may be the case in the rabbit, as claimed by Knaus, Reynolds and others, the evidence is conclusive that progesteronet augments the contractility of the human uterus.2-4 Braxton Hicks,” in 1871, demonstrat,ed by abdominal and vaginal palpation that the human uterus undergoes spontaneous intermittent contractions throughout pregnancy. Schatz,6 in the following year, published the first records of labor pains obtained by means of an intrauterine bag. This method has since been used successfully by a number of workers in studying the effects of drugs on the puerperal uterus. The bag, however, is not a pract.icaI means of recording the contractions of the pregnant uterus because of the danger of abortion and infection. Technical