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Relation between birth weight and blood pressure is independent of maternal blood pressure

BMJ 1998; 317 doi: (Published 05 September 1998) Cite this as: BMJ 1998;317:680
  1. Stephanie J C Taylor, Honorary research fellow.,
  2. Katherine Hird, Clinical research fellow,
  3. Peter Whincup, Reader in clinical epidemiology,
  4. Derek Cook, Reader in epidemiology.
  1. Department of Primary Care and Population Sciences, Royal Free Hospital School of Medicine, London NW3 2PF
  2. Department of Public Health Sciences, St George's Hospital Medical School, London SW17 0RE

    EDITOR—Walker et al conclude that the now well established inverse association between birth weight and blood pressure may in part be explained by hereditary factors.1 They suggest that low birth weight is a feature of an inherited predisposition to hypertension, perhaps because it is associated with higher maternal blood pressure during pregnancy.

    We have examined the influence of maternal blood pressure during pregnancy on the association between birth weight and blood pressure in a study of 8-11 year old children in 10 British towns. 2 3 Detailed antenatal and birth records were located for 1573 singleton children born in the town in which blood pressure was later measured; 1494 included blood pressure measurements during pregnancy. Although maternal systolic blood pressures at both 28 weeks' and 36 weeks' gestation were correlated with childhood systolic pressure at 8-11 years (correlation coefficients 0.16 and 0.14 respectively; P<0.0001), neither measure was correlated with birth weight (correlation coefficients 0.01).

    We also examined the effect of adjustment for maternal blood pressure on the relation between birth weight and blood pressure (table). Results are presented for the sexes together and for girls alone because we previously noted that the association between birth weight and blood pressure was concentrated among girls and only weakly present among boys at this age.2 Adjustment for maternal blood pressure at 36 weeks' gestation did not influence the size or the significance of the association between birth weight and blood pressure, either for all children or for girls alone. Similar results were seen after adjustment for antenatal blood pressure at 12, 18, and 28 weeks (data not shown).

    Associations between birth weight and systolic blood pressure summarised as regression coefficients, showing effect of adding maternal blood pressure at 36 weeks' gestation to multiple regression model*

    View this table:

    There is no doubt that in severe maternal hypertension in pregnancy the birth weight of the child is reduced.4 Our data suggest that there is little or no association between maternal blood pressure and birth weight in the general population and that, at least in children, the relation between birth weight and blood pressure is strongly independent of maternal blood pressure.