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Pre-pregnancy body mass index and breastfeeding initiation, early cessation and longevity: evidence from the first wave of the UK Millennium Cohort Study
  1. Tammy Campbell1,
  2. Nichola Shackleton2,3
  1. 1 Centre for Analysis of Social Exclusion, London School of Economics, London, UK
  2. 2 Centre of Methods and Policy Application in the Social Sciences (COMPASS), Faculty of Arts, University of Auckland, Auckland, New Zealand
  3. 3 Department of Statistics, Faculty of Science, University of Auckland, Auckland, New Zealand
  1. Correspondence to Dr Tammy Campbell, Centre for Analysis of Social Exclusion, London School of Economics, London WC2A 2AE, UK; t.campbell1{at}


Background International evidence indicates relationships between pre-pregnancy body mass index (BMI) and breastfeeding behaviours. This study aims to assess associations between key points in the breastfeeding trajectory (initiation, early cessation and longevity) and pre-pregnancy BMI in a recent, nationally representative British cohort. It also aims to explore in the British context potential moderation by mothers’ ethnic group.

Methods The sample comprises 17 113 mothers from the UK Millennium Cohort Study who have information on pre-pregnancy BMI. Associations between pre-pregnancy BMI categories and breastfeeding initiation, early cessation and longevity are tested using logistic regression. Directed acyclic graphics identify appropriate minimal adjustment to block biasing pathways and classify total and direct effects.

Results After adjusting for confounders, there are large differences in breastfeeding early cessation and longevity by pre-pregnancy BMI group. Differences in propensity to initiation are negligible. Having begun breastfeeding, overweight and obese mothers are more likely to cease in the first week and less likely to continue past 4 months. Observed potential mediators within pregnancy and delivery provide little explanation for relationships. Evidence for moderation by ethnicity is scant.

Conclusions The causal mechanisms underlying relationships between pre-pregnancy overweight, obesity, and breastfeeding behaviours require further research. However, this study suggests pre-pregnancy BMI as one predictive measure for targeting support to women less likely to establish breastfeeding in the early days, and to continue beyond 4 months. The nature of support should carefully be considered and developed, with mind to both intended and potential unintended consequences of intervention given the need for additional investigation into the causes of associations.

  • breastfeeding
  • obesity
  • perinatal
  • longitudinal

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  • TC and NS contributed equally.

  • Contributors Both authors contributed equally to this paper.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Disclaimer All views and interpretations expressed in this article are the authors’ own.

  • Competing interests None declared.

  • Patient consent Not required.

  • Ethics approval Because this study is a secondary data analysis, research ethics approval was not required. The first wave of the Millennium Cohort Study received ethics approval from National Health Service Ethical Authority in February 2001 (MREC/01/6/19).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement Not applicable; this is secondary data.