A hypothesis to explain the occurence of inner myometrial laceration causing massive postpartum hemorrhage.

BACKGROUND

Inner myometrial lacerations were found in three patients who developed uncontrollable postpartum massive bleeding despite the usual treatment for uterine atony. Because all the patients suffered from hemorrhage shock and their medical status deteriorated, their uteri were surgically removed to stop bleeding. After removal, one of them died. Postpartum hemorrhage was caused by inner myometrial laceration. We hypothesized a cause of inner myometrial laceration, using the three resected uteri, an assumed model of the uterine body, and 34 women.

METHODS

The subjects were 37 women, of whom three were patients with inner myometrial laceration, 23 were women without inner myometrial laceration who underwent cesarean section, and 11 were women in the first stage of labor. The three resected uteri were examined both macroscopically and microscopically. We measured the thickness of the wall of the uterine muscle at the widest point of the uterine corpus and the thickness of the myometrial wall at a transverse section of the uterine cervix, as well as the radius of the inner lumen at the widest point of the uterus in 23 women during cesarean section. We also measured the thickness of the myometrial wall at the widest point of the uterine corpus in 11 women at the end of the first stage of labor during ultrasonic examination. The data were then used to estimate the stress on the uterine muscle.

RESULTS

The stress on the uterine cervix was stronger than that on the uterine corpus during labor. When the stress on the uterine muscle is stronger than a specific value, inner myometrial lacerations develop on the right and/or left side of the uterine cervix. These lacerations may involve large vessels.

CONCLUSIONS

We have discovered another cause of postpartum hemorrhage which we have named inner myometrial laceration. These lacerations appeared to result from a strong stress on the uterine cervix caused by an abnormal rise in intrauterine pressure during labor.