Ultrasonic demonstration of local myometrial thickening in early intrauterine pregnancy.

In a group of women in the first and early second trimesters of pregnancy, local thickening of a limited region of the myometrium was observed ultrasonically. This prospective study aimed to evaluate the incidence and nature of this phenomenon. Local myometrial thickening was observed in 72 women out of 5521 examined (1.3%). Twenty-two were given ritodrine hydrochloride 10 mg by mouth, and 46 were monitored for up to 60 min without treatment. The local myometrial thickening in the ritodrine hydrochloride-treated group disappeared in 21 out of 22 women (95.5%) compared with the observed group, where the phenomenon disappeared in only 37 women (80.4%). Local myometrial thickenings probably represent transient uterine contractions; they tend to appear early in pregnancy, are prolonged, and may respond to ritodrine hydrochloride.