title: Measurement of cord insulin and insulin-related peptides suggests that girls are more insulin resistant than boys at birth.
abstract: OBJECTIVE
  We aimed to examine sex differences in insulin and insulin propeptide concentrations at birth using validated cord blood collection.
  
  
  METHODS
  We tested the impact on insulin and insulin propeptides of taking 13 cord blood samples in heparin and EDTA and then centrifuging and separating plasma after 1, 2, 24, or 48 h at room temperature (heparin) or 4 degrees C (EDTA). Cord plasma insulin and insulin propeptides concentrations were measured in 440 babies and correlated with offspring anthropometry measured at birth.
  
  
  RESULTS
  Cord insulin concentrations significantly decreased (74% those at baseline by 24 h; P = 0.01) in the samples taken in heparin and stored at room temperature, but those taken on EDTA and refrigerated remained stable for up to 48 h. Insulin propeptides were stable in both. Cord plasma insulin and insulin propeptides measured in EDTA were related to all measures of birth size and maternal glycemia and BMI (r > 0.11; P < 0.03 for all) and were higher in those delivered via caesarean section. Girls were lighter (3,497 vs. 3,608 g; P = 0.01) but had higher cord insulin (46.7 vs. 41.2 pmol/l; P = 0.031), total proinsulin (34.1 vs. 25.8 pmol/l; P < 0.001), and intact proinsulin (9.5 vs. 8.3 pmol/l; P = 0.004) concentrations than boys; this was further confirmed when cord insulin concentrations of boys and girls were compared after pair matching for birth weight (insulin 49.7 vs. 42.1 pmol/l; P = 0.004).
  
  
  CONCLUSIONS
  When using appropriate sample collection methods, female newborns have higher insulin concentrations than male newborns, despite being smaller, suggesting intrinsic insulin resistance in girls.
authors.affiliation: Diabetes Research, Peninsula Medical School, Exeter, UK.
authors.forename: Beverley M
authors.initials: BM
authors.lastname: Shields
authors.forename: Bridget
authors.initials: B
authors.lastname: Knight
authors.forename: Heather
authors.initials: H
authors.lastname: Hopper
authors.forename: Anita
authors.initials: A
authors.lastname: Hill
authors.forename: Roy J
authors.initials: RJ
authors.lastname: Powell
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Hattersley
authors.forename: Penelope M
authors.initials: PM
authors.lastname: Clark
mesh_terms: D001800:Blood Specimen Collection; D005260:Female; D005312:Fetal Blood / Q000737:chemistry*; D006801:Humans; D007231:Infant, Newborn; D007328:Insulin / Q000097:blood*; D007333:Insulin Resistance; D008297:Male; D012727:Sex Characteristics
chemical_list: D007328:Insulin