Contractions of the inner third of the myometrium.

Forty-six consecutive endovaginal ultrasound examinations were screened for the presence of myometrial contractions. The study group contained pregnant women up to 10 weeks' menstrual age, nonpregnant, and postmenopausal women. Rhythmic myometrial contractions of the inner myometrial third not previously reported were seen in 35 studies in pregnant, nonpregnant, and postmenopausal women. The contractions involved the inner third of the myometrium in all but two cases. In these two cases, all three muscular layers were involved. The majority of women showed retrograde contractions, with the contraction wave moving from the cervix to the fundus. In menstruating women and one case of abortion, the contractions were antegrade. It is our speculation that these retrograde contractions of the inner myometrial third may be important in sperm transport and for the conservation of early pregnancies within the uterine cavity.