Prenatal measurement of testicular diameter by ultrasonography: development of fetal male gender and evaluation of testicular descent.

Prenatal ultrasonography has evolved through advancements in imaging technology and observer experience. The purpose of the present study was to evaluate fetal testicular descent and diameter in relation to gestational age. A prospective cross-sectional study on 331 fetuses from an unselected population underwent a detailed assessment of testicular descent and diameter at 20-40 weeks' gestation by means of transabdominal sonography (91.2%) and transvaginal sonography (8.8%) when necessary. Fetal gender was identified in the transverse and sagittal planes and maximum testicular diameter was measured. The mean testicular diameter (in millimeters) per week and the 95% confidence interval (CI) were defined. Testicular descent was not observed prior to 23 weeks' gestation, with 6.6% of the fetuses having one testis descended at 23 weeks and 98.2% after 32 weeks. A linear relationship between testicular diameter and gestational age was observed. The present results chart the time course for testicular descent and provide a centile chart for fetal testicular diameter from 25 to 40 weeks' gestation. These findings may aid prenatal diagnosis of associated abnormal conditions as well as investigations into the clinical finding of abnormal testicular size.