title: Changes in calcitropic hormones, bone markers and insulin-like growth factor I (IGF-I) during pregnancy and postpartum: a controlled cohort study.
abstract: Pregnancy and lactation cause major changes in calcium homeostasis and bone metabolism. This population-based cohort study presents the physiological changes in biochemical indices of calcium homeostasis and bone metabolism during pregnancy and lactation
  
  
  BACKGROUND
  We describe physiological changes in calcium homeostasis, calcitropic hormones and bone metabolism during pregnancy and lactation.
  
  
  METHODS
  We studied 153 women planning pregnancy (n=92 conceived) and 52 non-pregnant, age-matched female controls. Samples were collected prior to pregnancy, once each trimester and 2, 16 and 36 weeks postpartum. The controls were followed in parallel.
  
  
  RESULTS
  P-estradiol (E2), prolactin and 1,25-dihydroxyvitamin D (1,25(OH)2D) increased (p<0.001) during pregnancy, whereas plasma levels of parathyroid hormone (P-PTH) and calcitonin decreased (p<0.01). Insulin-like growth factor I (IGF-I) was suppressed (p<0.05) in early pregnancy but peaked in the third trimester. Postpartum, E2 was low (p<0.05); prolactin decreased according to lactation status (p<0.05). 1,25(OH)2D was normal and IGF-I was again reduced (p<0.05). P-PTH and calcitonin increased postpartum. From early pregnancy, markers of bone resorption and formation rose and fall, respectively (p<0.001). From the third trimester, bone formation markers increased in association with IGF-I changes (p<0.01). Postpartum increases in bone turnover markers were associated with lactation status (p<0.001). During lactation, plasma phosphate was increased, whereas calcium levels tended to be decreased which may stimulate PTH levels during and after prolonged lactation.
  
  
  CONCLUSIONS
  The increased calcium requirements in early pregnancy are not completely offset by increased intestinal calcium absorption caused by high 1,25(OH)2D since changes in bone markers indicated a negative bone balance. The rise in bone formation in late pregnancy may be initiated by a spike in IGF-I levels. The high bone turnover in lactating women may be related to high prolactin and PTH levels, low E2 levels and perhaps increased parathyroid hormone-related protein levels.
authors.affiliation: Department of Endocrinology and Internal Medicine, Aarhus University Hospital, and Department of Clinical Medicine, Faculty of Health Sciences, Aarhus University, Tage Hansens Gade 2, 8000, Aarhus C, Denmark. kristine.moller@ki.au.dk
authors.forename: U K
authors.initials: UK
authors.lastname: Møller
authors.forename: S
authors.initials: S
authors.lastname: Streym
authors.forename: L
authors.initials: L
authors.lastname: Mosekilde
authors.forename: L
authors.initials: L
authors.lastname: Heickendorff
authors.forename: A
authors.initials: A
authors.lastname: Flyvbjerg
authors.forename: J
authors.initials: J
authors.lastname: Frystyk
authors.forename: L T
authors.initials: LT
authors.lastname: Jensen
authors.forename: L
authors.initials: L
authors.lastname: Rejnmark
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D016723:Bone Remodeling / Q000502:physiology; D001842:Bone and Bones / Q000378:metabolism*; D002116:Calcitonin / Q000097:blood; D002118:Calcium / Q000097:blood; D016022:Case-Control Studies; D004958:Estradiol / Q000097:blood; D005260:Female; D006706:Homeostasis / Q000502:physiology; D006728:Hormones / Q000097:blood*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007774:Lactation / Q000097:blood; D010012:Osteogenesis / Q000502:physiology; D010281:Parathyroid Hormone / Q000097:blood; D049590:Postpartum Period / Q000097:blood* / Q000502:physiology; D011247:Pregnancy / Q000097:blood* / Q000502:physiology; D011388:Prolactin / Q000097:blood; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood
chemical_list: D015415:Biomarkers; D006728:Hormones; D010281:Parathyroid Hormone; D014807:Vitamin D; D004958:Estradiol; C097949:1,25-dihydroxyvitamin D; D007334:Insulin-Like Growth Factor I; D011388:Prolactin; D002116:Calcitonin; D002118:Calcium