title: Gender difference in breast tissue size in infancy: correlation with serum estradiol.
abstract: Breast tissue in newborn infants is considered to be physiologic and mainly related to exposure to maternal hormones in utero or through breast-feeding. However, controversy exists as to whether breast tissue in later infancy is under the influence of endogenous hormones. Children at 2-4 mo of age have a surge of reproductive hormones, including estradiol, which may affect the mammary gland. In a prospective cohort study of 1126 healthy, 3-mo-old infants, breast tissue size and reproductive hormones were measured. We found that palpable breast tissue (diameter >or=3 mm) is a common physiologic condition present in 78.9% of children, significantly more frequent (p < 0.001) and larger (p < 0.001) in girls than in boys. Girls had significantly higher median estradiol levels than boys (30.0 versus 21.0 pmol/L, p < 0.001). In a multiple regression model including breast tissue size given as quartiles as the dependent variable and weight for gestational age, subscapular skinfold, weight at 3 mo of age and serum estradiol as independent variables, a gender difference was shown. In girls, the estradiol level was positively (p < 0.03) correlated to breast quartile. In boys, no correlations were found. Whether the stimulation of the mammary gland in infancy represents a developmental window that is of biologic significance for breast development and pathology in adulthood remains to be defined.
authors.affiliation: University Department of Growth and Reproduction, Rigshospitalet, Copenhagen, Denmark. rh03096@rh.dk
authors.forename: Ida Maria
authors.initials: IM
authors.lastname: Schmidt
authors.forename: Marla
authors.initials: M
authors.lastname: Chellakooty
authors.forename: Anne-Maarit
authors.initials: AM
authors.lastname: Haavisto
authors.forename: Kirsten Arntz
authors.initials: KA
authors.lastname: Boisen
authors.forename: Ida Norgil
authors.initials: IN
authors.lastname: Damgaard
authors.forename: Ulla
authors.initials: U
authors.lastname: Steendahl
authors.forename: Jorma
authors.initials: J
authors.lastname: Toppari
authors.forename: Niels Erik
authors.initials: NE
authors.lastname: Skakkebaek
authors.forename: Katharina Maria
authors.initials: KM
authors.lastname: Main
mesh_terms: D000886:Anthropometry; D001940:Breast / Q000033:anatomy & histology* / Q000254:growth & development; D015331:Cohort Studies; D004958:Estradiol / Q000097:blood*; D005260:Female; D005387:Finland; D005865:Gestational Age; D006801:Humans; D007223:Infant; D008297:Male; D011446:Prospective Studies; D012727:Sex Characteristics; D012885:Skinfold Thickness; D013739:Testosterone / Q000097:blood
chemical_list: D013739:Testosterone; D004958:Estradiol