Inherent sources of ultrasound variability in relation to follicular measurements

Determination of ovarian follicular size and number by real-time ultrasound lacks the precision that has been ascribed to it. Four major error sources inherent in the scanning and interpreting process were analyzed to determine the relative contributions to overall variation. The sources measured were machine, sonographer, sonologist, and patient bladder volume. A protocol using a normal clomiphene-stimulated woman allowed the determination of the coefficient of variance for both follicular number and follicular diameter as well as a mean diameter range in each of the categories. A large degree of variation was found in all groups. Surprisingly, it was noted that maximal bladder filling did not produce optimal images. We believe that while variability in ultrasound can be recognized and lessened, it cannot be eliminated. Thus, caution must be used when ultrasound follicular comparisons are made within each program from day to day and particularly between institutions. A liberal range should be allowed for optimal follicle sizes for any given stimulation protocol.