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Effect of reducing caffeine intake on birth weight and length of gestation: randomised controlled trial

BMJ 2007; 334 doi: (Published 22 February 2007) Cite this as: BMJ 2007;334:409
  1. Bodil Hammer Bech, assistant professor1,
  2. Carsten Obel, assistant professor1,
  3. Tine Brink Henriksen, consultant2,
  4. Jørn Olsen, professor3
  1. 1Institute of Public Health, Department of Epidemiology, University of Aarhus, 8000 Aarhus, Denmark
  2. 2Perinatal Epidemiology Research Unit, Aarhus University Hospital, Skejby, Denmark
  3. 3Department of Epidemiology, University of California, Los Angeles, USA
  1. Correspondence to: B H Bech bhb{at}
  • Accepted 28 November 2006


Objective To estimate the effect of reducing caffeine intake during pregnancy on birth weight and length of gestation.

Design Randomised double blind controlled trial.

Setting Denmark.

Participants 1207 pregnant women drinking at least three cups of coffee a day, recruited before 20 weeks' gestation.

Interventions Caffeinated instant coffee (568 women) or decaffeinated instant coffee (629 women).

Main outcome measures Birth weight and length of gestation.

Results Data on birth weight were obtained for 1150 liveborn singletons and on length of gestation for 1153 liveborn singletons. No significant differences were found for mean birth weight or mean length of gestation between women in the decaffeinated coffee group (whose mean caffeine intake was 182 mg lower than that of the other group) and women in the caffeinated coffee group. After adjustment for length of gestation, parity, prepregnancy body mass index, and smoking at entry to the study the mean birth weight of babies born to women in the decaffeinated group was 16 g (95% confidence interval −40 to 73) higher than those born to women in the caffeinated group. The adjusted difference (decaffeinated group−caffeinated group) of length of gestation was −1.31 days (−2.87 to 0.25).

Conclusion A moderate reduction in caffeine intake in the second half of pregnancy has no effect on birth weight or length of gestation.

Trial registration Clinical Trials NCT00131690.


  • We thank the women who participated in the study, J Sønderskov for her support, and M Vaeth for statistical advice.

  • Contributors: BHB, CO, TBH, and JO designed and initiated the trial. BHB, CO, and TBH coordinated the trial, and BHB analysed the data. All authors met regularly and contributed to trial management; all participated in the interpretation of results and in the writing of the paper. BHB is the guarantor.

  • Funding: The project is supported by a grant from the Health Insurance Foundation (No 1105-93 and 11099-96). The Danish National Research Foundation established the Danish Epidemiology Science Centre that initiated and created the Danish national birth cohort. The birth cohort is furthermore a result of a major grant from this foundation. Additional support for the birth cohort was obtained from the Pharmacy Foundation, the Egmont Foundation, the March of Dimes Birth Defects Foundation, and the Augustinus Foundation. Nestlé was not involved in the design, analyses, or writing of this paper.

  • Competing interests: None declared.

  • Ethical approval: This study was approved by regional science ethics committees in Denmark and the Danish Data Protection Agency.

  • Accepted 28 November 2006
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