title: Fetal thyroid hormone level at birth is associated with fetal growth.
abstract: BACKGROUND
  Thyroid function is known to play an important role in fetal neurological development, but its role in regulating fetal growth is not well established. Overt maternal and fetal thyroid disorders are associated with reduced birth weight. We hypothesized that, even in the absence of overt thyroid dysfunction, maternal and fetal thyroid function influence fetal growth.
  
  
  OBJECTIVE
  In normal, healthy pregnancies, we aimed to assess whether fetal thyroid hormone at birth (as measured in cord blood) is associated with fetal growth. We also aimed to study whether fetal thyroid hormone at birth is associated with maternal thyroid hormone in the third trimester.
  
  
  METHODS
  In 616 healthy mother-child pairs, TSH, free T(4) (FT4), and free T(3) (FT3) were measured in mothers at 28 wk gestation and in umbilical cord blood at birth. Birth weight, length, head circumference, and tricep and bicep skinfold thicknesses were measured on the babies.
  
  
  RESULTS
  Cord FT4 was associated with birth weight (r = 0.25; P < 0.001), length (r = 0.17; P < 0.001), and sum of skinfolds (r = 0.19; P < 0.001). There were no associations between birth measurements and either cord TSH or cord FT3. Maternal FT4 and cord FT4 were correlated (r = 0.14; P = 0.0004), and there were weaker negative associations between maternal TSH and cord FT4 (r = -0.08; P = 0.04) and FT3 (r = -0.10; P = 0.01).
  
  
  CONCLUSIONS
  Associations between cord FT4 and birth size suggest that fetal thyroid function may be important in regulating fetal growth, both of skeletal size and fat. The correlation between third-trimester maternal FT4 and cord FT4 supports the belief that maternal T(4) crosses the placenta even in late gestation.
authors.affiliation: Peninsula National Institute for Health Research Clinical Research Facility, Peninsula Medical School, University of Exeter, Exeter EX2 5DW, United Kingdom.
authors.forename: Beverley M
authors.initials: BM
authors.lastname: Shields
authors.forename: Beatrice A
authors.initials: BA
authors.lastname: Knight
authors.forename: Anita
authors.initials: A
authors.lastname: Hill
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Hattersley
authors.forename: Bijay
authors.initials: B
authors.lastname: Vaidya
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001724:Birth Weight / Q000502:physiology; D005260:Female; D005312:Fetal Blood; D047109:Fetal Development / Q000502:physiology*; D006801:Humans; D007118:Immunoassay; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D011263:Pregnancy Trimester, Third / Q000097:blood; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000502:physiology; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*
chemical_list: D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine