Establishment of Normative Data for the Amount of Breast Tissue Present in Healthy Children up to Two Years of Age

Objective: To establish a set of normal values for breast size in children up to two years of age, and to assess the effects of gender, gestational age, and type of feeding and growth parameters on breast size. Design: Prospective cohort study over 20 months Setting: The Mayo Clinic Rochester, MN, neonatal nursery and Community Pediatrics Clinic. Participants: Well term infants and children through two years of age. Interventions: Measurement of breast size based on previously described methods to yield a figure called the breast unit. Main outcome measure: Transformation of breast unit size into percentiles according to age. Results: The 50(th) to 99(th) percentiles for 810 healthy term Caucasian infant visits were calculated. The 50th breast unit percentile was similar in males and females at birth and declined with age following a quadratic relationship for females and a cubic relationship for males. Breast tissue in female infants remained larger and persisted longer. Palpable breast tissue was still present in 45.2% of male and 61.6% of female visits after 10 months of age. At age 18 months, 5% of girls had a breast size unit greater than 2.88 cm(2) and 5% of boys had a breast size unit greater than 1.00 cm2. Conclusions: These data allow creation of normal standards of breast size for age, which could provide a future clinical tool to assist clinicians in the evaluation of early childhood breast enlargement in similar populations.