Size of testes, ovaries, uterus and breast buds by ultrasound in healthy full-term neonates ages 0–3 days

Background Hormonally sensitive organs in the neonate can change size within days of birth as circulating maternal estrogen wanes. Although several reports document the size of these organs through infancy, few focus attention on the near-birth period. Clinical and research evaluation of hormonal and genitourinary disorders would benefit from reference size standards. Objective We describe the size of the uterus, ovaries, testes and breast buds in healthy term neonates. Materials and methods As part of the Infant Feeding and Early Development (IFED) study, we sonographically measured the largest diameter of these organs in sagittal, transverse and anterior-posterior planes for 194 female and 204 male newborns up to 3 days old. We calculated mean, median and percentiles for longest axis length and for volume calculated from measured diameters. We evaluated size differences by laterality, gender and race and compared our observations against published values. Results Mean length and mean volume were as follows: uterus, 4.2 cm and 10.0 cm 3 ; ovary, 1.0 cm and 0.2 cm 3 ; testis, 1.1 cm and 0.3 cm 3 (0.4 cm 3 Lambert volume); female breast bud, 1.2 cm and 0.7 cm 3 ; male breast bud, 1.1 cm and 0.6 cm 3 . Breast buds were larger in females than males. Laterality differences were typically below the precision of clinical measurement. No significant race differences were detected. Conclusion Using data from our large cohort together with published values, we provide guidelines for evaluating the size of reproductive organs within the first 3 days of age. Discrepancies between our results and published values are likely attributable to technique.