Objective: To evaluate the accuracy of a formula combining the prolate ellipsoid (uterine corpus) and cylinder (uterine cervix) formulas in estimating the preoperative weight of the total uterus using a transvaginal ultrasound probe to obtain the uterine dimensions for the formulas.
Study design: Three dimensions of the uterine corpus (length, width and anteroposterior diameter) and cervical length and cervical anteroposterior diameter were preoperatively determined using a transvaginal ultrasound probe in 12 women with symptomatic leiomyomas scheduled to undergo hysterectomy. In two patients whose uteruses were the largest, part of the measurements had to be taken with a transabdominal ultrasound. Three investigators repeated all the rounds of measurements three times, producing in total 108 of findings (12 subjects x 3 investigators x 3 rounds of measurements). The geometric formula of prolate ellipsoid was compared to a formula combining the ellipsoid and cylinder formulas for accuracy in predicting overall uterine size (corpus and cervix) through correlation with hysterectomy specimens. The weight of the uterus in grams was directly derived from the volume of the uterus.
Results: All measurements of the uterine corpus and cervix could be obtained preoperatively with a transvaginal ultrasound probe except in two patients who had the largest uteruses. The plain, traditional formula for the prolate ellipsoid overestimated the weight of the uterus and differences between the estimated and the true weight were statistically significant. The difference was not significant when the formula combining the formulas of the prolate ellipsoid and cylinder was used.
Conclusion: The new formula combining the prolate ellipsoid and cylinder formulas is more accurate in predicting the true total weight of the uterus than the plain prolate ellipsoid formula. The transvaginal ultrasound probe proved useful in evaluating the dimensions of the uterine corpus and cervix.