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Are observed associations between a high maternal prepregnancy body mass index and offspring IQ likely to be causal?
  1. Helen Coo1,
  2. Leandre Fabrigar2,
  3. Gregory Davies3,
  4. Renee Fitzpatrick4,
  5. Michael Flavin1
  1. 1Pediatrics, Queen's University, Kingston, Ontario, Canada
  2. 2Psychology, Queen's University, Kingston, Ontario, Canada
  3. 3Obstetrics & Gynaecology, Queen's University, Kingston, Ontario, Canada
  4. 4Psychiatry, Queen's University, Kingston, Ontario, Canada
  1. Correspondence to Helen Coo, Pediatrics, Queen's University, Kingston, ON K7L 3N6, Canada; cooh{at}


Background A high maternal prepregnancy body mass index has been associated with lower offspring IQ, but it is unclear if the relationship is causal. To explore this, our objectives were to compare maternal and paternal estimates and to assess whether certain factors mediate the association.

Methods We analysed data from the Avon Longitudinal Study of Parents and Children, which initially recruited 14 541 women residing in Avon, UK, with an expected date of delivery in 1991–1992. Data were collected during and after pregnancy by questionnaire, medical record abstraction and clinical assessment. At approximately 8 years of age, psychologists administered an abbreviated form of the Wechsler Intelligence Scale for Children-III. We fit multivariable logistic regression models to estimate parental prepregnancy obesity and overweight–offspring IQ associations. Counterfactually defined indirect (mediated) effects of maternal prepregnancy obesity on offspring IQ were estimated through path analysis.

Results Among 4324 mother–father–child triads and using normal weight as the referent, we observed consistently stronger associations for maternal prepregnancy obesity and offspring performance IQ (eg, adjusted β (95% CI)=−3.4 (−5.7 to −1.2) vs −0.97 (−2.9 to 0.96) for paternal obesity). The indirect effects of maternal obesity on offspring IQ through pathways involving gestational weight gain and duration of breastfeeding were small but significant.

Conclusion Our findings are consistent with a weak biologic effect of maternal adiposity in pregnancy on offspring performance IQ. Given the growing prevalence of obesity worldwide, more evidence is needed to resolve the correlation versus causation debate in this area.

  • child health
  • cognition
  • pregnancy
  • obesity

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  • Contributors HC: concept, design, analysis, interpretation, drafting and critical revision. LF: design, analysis, interpretation and critical revision. GD, RF and MF: design, interpretation and critical revision.

  • Funding This analysis was supported by a grant from the Queen’s University Department of Pediatrics Development and Innovation Fund.

  • Disclaimer This publication is the work of the authors, who will serve as guarantors for the contents of this paper.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval Ethical approval for the study was obtained from the Avon Longitudinal Study of Parents and Children (ALSPAC) Ethics and Law Committee and the Local Research Ethics Committees, as well as from the Queen’s University Health Sciences and Affiliated Teaching Hospitals Research Ethics Board (#6013816; PAED-363-14).

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

  • Data availability statement Data may be obtained from a third party and are not publicly available.