title: Unexpected changes in maternal breast size during pregnancy in relation to infant sex: an evolutionary interpretation.
abstract: OBJECTIVE
  This study evaluated changes in breast size during pregnancy depending on infant sex. Due to larger nutritional needs during lactation, male infants may stimulate greater changes in maternal breast size than female infants.
  
  
  METHODS
  Data were collected by an online questionnaire survey of 120 women from Poland, who had at least one child.
  
  
  RESULTS
  Changes in breast circumference during pregnancy were associated with the infant's gender. Surprisingly, mothers of female infants had greater breast circumference changes than the mothers of male infants (P = 0.03).
  
  
  CONCLUSIONS
  The observed difference is surprising in the light of studies reporting that mothers of male infants produced milk that had greater energy content. However, breast size alone does not determine the quality and quantity of produced milk. It is suggested that the larger difference in breast size for mothers of female infants results from a trade-off between direct energy allocations to the growing fetus and to breast enlargement. Perhaps, as in other primates maintaining sexually attractive attributes during pregnancy, early breast enlargement in women is a primary sexual stimulus. The ultimate function of early breast enlargement may function to ensure greater involvement from partners, which is especially important to mothers expecting daughters, who might be in poorer nutritional condition, as predicted by Trivers-Willard hypothesis.
authors.affiliation: Department of Epidemiology and Population Studies, Jagiellonian University Medical College, Krakow, Poland. agalbarczyk@gmail.com
authors.forename: Andrzej
authors.initials: A
authors.lastname: Galbarczyk
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001940:Breast / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D020407:Internet; D007774:Lactation; D011044:Poland; D011247:Pregnancy; D039401:Prenatal Nutritional Physiological Phenomena / Q000502:physiology*; D012016:Reference Values; D057566:Self Report; D012923:Social Class; D013223:Statistics as Topic; D011795:Surveys and Questionnaires; D013997:Time Factors; D055815:Young Adult