Updated reference values in pelvic ultrasonography for a Spanish population of healthy girls between 6 and 12 years old

Background: Pelvic ultrasonography (PUS) of the uterus and ovaries allows the diagnosis of changes in sexual development. However, the reference values used in Spain originate from old studies conducted in other countries. Objective: To determine reference uterine and ovarian measurements by PUS and according to pubertal status and bone age in a Spanish population of healthy girls aged between 6 and 12 years. Materials and methods: Descriptive cross-sectional study performed on 221 healthy girls from 2017 to 2019. Ovarian and uterine measurements were described and associated with chronological age, bone age, and Tanner stage. ROC curves were used to assess the predictive value of tests for Tanner stage II. Results: We described reference values for all PUS uterine and ovarian measurements assessed. Subjects in Tanner II (thelarche) had a mean age of 9.7 years (SD = 1.1) and mean BMI of 19.2 kg/m ². Fundal–cervical ratio changed from 1:1 to 2:1 at 12 years of chronological age (62.5% with 1:1 ratio; p < 0.0001) and 13 years of bone age (2:1 in 85.71%, p < 0.0001). Mean uterine length for Tanner II was 4.065 cm (SD = 0.736); mean ovarian volume was 2.466 cm ³ (SD = 1.719). Bone age, ovarian volume, and uterine length were good predictors of Tanner stage II. Conclusion: This is the first study providing reference uterine and ovarian PUS values in a Spanish population of healthy girls aged 6 to 12 years. Use of updated data characteristic of a specific population increases the diagnostic accuracy.