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Correction: Randomised controlled trial of oxytocin alone versus oxytocin and ergometrine in active management of third stage of labour

Further research is needed to elucidate the factors related to these differences. The effect of birth weight on blood pressure in early infancy or on subsequent weight does not entirely explain the effect of birth weight at 4 years as birth weight remained importantly related to blood pressure after adjustment for these variables. Prenatal factors, such as hormonal environment, matemal diet, and genetic predisposition, or postnatal factors, such as infant diet and pattem of activity, should be studied as factors that set or maintain blood pressure at a fairly high level. The relevance of these and similar findings to understanding the development of pathophysiology later in life remains debatable. In the absence of longitudinal studies from childhood to adulthood we can only postulate a link between early and later pattems of blood pressure from studies on tracking blood pressure, family history of hypertension, and the physiology of blood pressure in children."'S If childhood experiences are associated with events later on in life, as studies seem to indicate, then our findings lead us to suggest a U shaped relation between birth weight and later onset of disease in healthy cohorts, with high birthweight infants and a subset of low birthweight infants being at increased risk. This U shaped relation is in contrast to the model proposed by Barker and Martyn, who, on the basis of their findings, concluded that the risk for subsequent cardiovascular disease is inversely and linearly related to birth weight.2 Our cohort was not selected on the basis of birth weight, was healthy at birth, and grew up in a fairly homogeneous middle class environment. This sample contained few infants bom before 37 weeks (1-2%) and few of birth weight less than or equal to 2500 g (1-0%). Barket et al, however, reported preterm rates of 3-7%4 and low birthweight rates of 3%1 and 10%5 in samples used to study the relation between birth weight and cardiovascular disease. The distribution of birth weight in a sample may influence the direction and importance of the relation between birth weight and adult outcomes if there are two different processes regulating blood pressure in low and high birthweight infants. Differences between low and high birthweight infants will also affect the outcome of studies on tracking blood pressure in infants and children.2223 In summary, we found that birth weight had a U shaped relation to blood pressure in 4 year old children. Further study of changes in blood pressure and weight in early infancy related to birth weight may help to elaborate this relation. Other factors should also be considered. Identification of these factors may eventually prove birth weight to be causally or noncausally related to disease outcomes in the future. A more refined conceptual model linking prenatal and postnatal events is needed to bring us closer to understanding the contribution of early childhood experiences to later adult diseases. Although this study was fairly small in size and of limited follow up, the results suggest that factors in early life that lead to high blood pressure need to be considered separately for low and high birthweight infants and that future research on this topic should take these differences related to birth weight into account.