Within pair association between birth weight and blood pressure at age 8 in twins from a cohort study
BMJ 1999; 319 doi: https://doi.org/10.1136/bmj.319.7221.1325 (Published 20 November 1999) Cite this as: BMJ 1999;319:1325
- Terence Dwyer, professor (T.Dwyer{at}utas.edu.au)a,
- Leigh Blizzard, biostatisticiana,
- Ruth Morley, senior research fellowb,
- Anne-Louise Ponsonby, public health physicianc
- a Menzies Centre for Population Health Research, University of Tasmania, Hobart 7001, Tasmania, Australia
- b Clinical Epidemiology and Biostatistics Unit, University of Melbourne Department of Paediatrics, Royal Children's Hospital, Melbourne, Victoria, Australia
- c Academic Unit of General Practice and Community Care, Canberra Clinical School, University of Sydney, Canberra, Australian Capital Territory, Australia
- Correspondence to: T Dwyer
- Accepted 19 July 1999
Abstract
Objectives: To study the association between birth weight and blood pressure in children from multiple pregnancies (multiplets), mostly twins, to determine whether maternal or genetic factors are responsible for the association.
Design: Cohort study.
Setting: Southern Tasmania.
Subjects: 888 children including 104 multiplets (32 monozygotic, 72 dizygotic).
Main outcome measure: Systolic blood pressure (mm Hg).
Results: Blood pressure decreased with birth weight and increased with current body mass. After adjustment for age and body mass, systolic blood pressure changed by −1.94 mm Hg (95% confidence interval −2.89 to −0.98) per 1 kg increase in birth weight of singletons. For multiplets, blood pressure changed by −7.0 mm Hg (−10.1 to −3.9) for each 1 kg increase in birth weight. This was little altered in within pair analyses (−5.3, −13.8 to 3.2) and was similar for both monozygotic (−6.5, −22.5 to 9.4) and dizygotic (−4.9, −15.8 to 6.0) pairs.
Conclusion: Because the association between birth weight and blood pressure was largely unchanged in within pair analyses, exposures originating in the mother (such as nutritional status) cannot be wholly responsible. The association also remained within monozygotic pairs, suggesting that genetic predisposition is not wholly responsible either. The principal causal pathway must concern mechanisms within the fetoplacental unit. The stronger association in multiplets suggests that factors adversely influencing both blood pressure and birth weight are more prevalent in multiple pregnancies.
Key messages
Low birthweight is associated with high blood pressure from an early age
Maternal factors, including diet during pregnancy, cannot wholly explain the association between fetal development and later risk of cardiovascular disease
Because the association between blood pressure and birthweight remained in monozygotic twins, genetic factors are unlikely to be responsible for the association
Important causes of the association seem to be operating within the fetoplacental unit during fetal life
Further research should now focus on placental function and fetal exposures
Footnotes
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Funding This study was funded by the National Health and Medical Research Council of Australia. The Tasmanian infant health survey was funded by the National Health and Medical Research Council of Australia, US National Institutes of Health (grant 001 HD28979-01A1, Tasmanian State Government, Australian Rotary Health Research Fund, Sudden Infant Death Syndrome Research Foundation, National Sudden Infant Death Syndrome Council of Australia, Community Organisations' support programme of the Department of Human Services and Health, Zonta International, Wyeth Pharmaceuticals, and Tasmanian Sanatoria After-Care Association. A-LP was supported by a National Health and Medical Research Council Public Health Research and Development Committee fellowship.
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Competing interests None declared.
- Accepted 19 July 1999