|Causes and Consequences of Intrauterine Growth Retardation, Proceedings of an IDECG workshop, November 1996, Baton Rouge, USA, Supplement of the European Journal of Clinical Nutrition (International Dietary Energy Consultative Group - IDECG, 1996, 100 pages)|
|Report of the IDECG group on variation in fetal growth and adult disease|
There is an established body of literature that size at birth is related to morbidity and mortality in infancy and to various neurodevelopmental outcomes and physical growth in childhood. The question of whether there are long-term effects on blood pressure and insulin mediated glucose uptake in childhood and disease in adulthood remains more controversial. On this question the working group reached a consensus that there is evidence for associations between fetal growth (as measured by birth weight, BW) and adult disease as follows:
- There is a negative association among both children and adults between BW within the normal range and blood pressure.
- There is a J-shaped negative association between BW and death from cardiovascular disease (CVD), and in particular from ischemic heart disease. This association is most securely established in men.
- There is a progressive negative association between BW or ponderal index at birth and non-insulin dependent diabetes mellitus (NIDDM).
- Birth weight is not associated with the aggregate of causes of mortality other than CVD, although there is some evidence for effects on other conditions including a negative association between BW and chronic respiratory disease and a direct association between BW and breast cancer.
- Nearly all these associations have been reported from studies in developed countries.
There are a number of uncertainties that surround these associations; they include:
- Whether they are confounded by factors that were present at birth and continue to act throughout the lifespan ('continuity of circumstance'), although recent data and research in progress suggest that this kind of confounding may not be a major issue.
- Whether the association between BW and CVD is as significant for women as for men.
- Whether the observed association between BW and CVD is dependent on established adult risk factors for CVD (e.g. blood pressure, serum cholesterol).
- Whether it is BW and/or other characteristics of size at birth (e.g. degree of adiposity, birth length, head circumference) that are important for these associations.
- Whether these associations occur to a greater or lesser degree in developing-country settings, where the distribution of BW and the predictors, of variation in fetal growth differ from those characteristic of developed-country settings.
The working group identified several issues that need to be taken into account when interpreting the observed associations between variation in fetal growth and adult disease; these include:
- Potential confounding factors that were not measured at all or that were measured imprecisely.
- The generalizability of findings from any single study within a selected population to the whole population and to other populations.
- The apparently opportunistic use of a range of different obstetric and perinatal measures as explanatory variables, and the over-interpretation of associations with these variables as distinct causal mechanisms.
- How the associations between variation in fetal growth and adult disease are to be reconciled with the secular trends and ecologic differences in BW and the incidence of CVD.