title: Relation of caffeine intake and blood caffeine concentrations during pregnancy to fetal growth: prospective population based study.
abstract: OBJECTIVE
  To examine the association of plasma caffeine concentrations during pregnancy with fetal growth and to compare this with relations with reported caffeine intake.
  
  
  METHODS
  Prospective population based study.
  
  
  METHODS
  District general hospital, inner London.
  
  
  METHODS
  Women booking for delivery between 1982 and 1984. Stored plasma was available for 1,500 women who had provided a blood sample on at least one occasion and for 640 women who had provided a sample on all three occasions (at booking, 28 weeks, and 36 weeks).
  
  
  METHODS
  Birth weight adjusted for gestational age, maternal height, parity, and sex of infant. The exposures of interest were reported caffeine consumption and blood caffeine concentration. Cigarette smoking was assessed by blood cotinine concentration.
  
  
  RESULTS
  Caffeine intake showed no changes during pregnancy, but blood caffeine concentrations rose by 75%. Although caffeine intake increased steadily with increasing cotinine concentration above 15 ng/ml, blood caffeine concentrations fell. Caffeine consumption was inversely related to adjusted birth weight, the estimated effect being a 1.3% fall in birth weight for a 1,000 mg per week increase in intake (95% confidence interval 0.5% to 2.1%). The apparent caffeine effect was confined to cigarette smokers, among whom the estimated effect was-1.6%/1000 mg a week (-2.9% to -0.2%) after adjustment for cotinine and -1.3% (-2.7% to 0.1%) after further adjustment for social class and alcohol intake. Adjusted birth weight was unrelated to blood caffeine concentrations overall (P = 0.09, but a positive coefficient), after adjustment for cotinine (P = 0.73), or among current smokers (P = 0.45).
  
  
  CONCLUSIONS
  Smokers consume more caffeine than non-smokers. Blood caffeine concentrations during pregnancy are not related to fetal growth, but caffeine intake is negatively associated with birth weight, with this effect being apparent only in smokers. The effect remains of borderline significance after adjustment for other factors. Prudent advice for pregnant women would be to reduce caffeine intake in conjunction with stopping smoking.
authors.affiliation: Department of Public Health Sciences, St George's Hospital Medical School, London.
authors.forename: D G
authors.initials: DG
authors.lastname: Cook
authors.forename: J L
authors.initials: JL
authors.lastname: Peacock
authors.forename: C
authors.initials: C
authors.lastname: Feyerabend
authors.forename: I M
authors.initials: IM
authors.lastname: Carey
authors.forename: M J
authors.initials: MJ
authors.lastname: Jarvis
authors.forename: H R
authors.initials: HR
authors.lastname: Anderson
authors.forename: J M
authors.initials: JM
authors.lastname: Bland
mesh_terms: D001628:Beverages; D001724:Birth Weight; D002099:Cacao; D002110:Caffeine / Q000008:administration & dosage / Q000097:blood* / Q000378:metabolism; D002253:Carbonated Beverages; D003069:Coffee; D004326:Drinking; D005314:Embryonic and Fetal Development / Q000187:drug effects*; D005260:Female; D006801:Humans; D011247:Pregnancy / Q000097:blood*; D011446:Prospective Studies; D012907:Smoking / Q000097:blood; D013662:Tea
chemical_list: D003069:Coffee; D013662:Tea; D002110:Caffeine