The possible impact of a myomatous uterus on the accuracy of fetal biometric measurements

Objective. The propagation speed of ultrasound beams changes in different media. The aim of the study was to assess the possible measurement error of fetal biometry performed in cases of myomatous uterus. Design. Three iron phantoms of 30 mm, 50 mm and 70 mm were measured by three different transducers of 3.5 MHz, 6.5 MHz and 7.5 MHz. Measurements were performed in a water bath and the intraobserver variability was assessed. Thereafter phantoms were measured with one of their edges covered by a specimen of myomatous uterus while their other edge was covered with water. Results. Artifactual lengthening of the phantom's size was observed in measurements performed with the uterine myoma. The measurement errors were inversely related to the length of the phantoms and became statistically significant in the phantoms of 30 mm (13.15 ± 3.16% without the myoma vs. 17.38 ± 4.39% with the myoma; p < 0.0001). Measurements errors were independent of the transducer type (p = 0.001, p = 0.01 and p = 0.014 for the 3.5-MHz, 6.5-MHz and 7.5-MHz transducers, respectively). Conclusions. Ultrasound measurement errors are expected while examining small fetal organs which are partially overshadowed by a myoma.