|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)|
|Effects of intrauterine growth retardation on mental performance and behavior, outcomes during adolescence and adulthood|
In follow-up studies of older children it becomes more and more difficult to separate prenatal and postnatal effects. Other major problems are diminishing statistical power and potential biases due to sample attrition.
Most studies of long-term outcomes of IUGR are relatively old. Considerable improvements have been made in the last few years in obstetric and emergency newborn care in industrialized countries. This means that the factors that recent survivors have been exposed to and the risks they entail could be substantially different from those of earlier study populations.
If head sparing can be observed in some IUGR babies, it is usually relative, i.e. head size is also affected, but to a lesser extent than weight and height. The extent to which head size is reduced seems closely related to the degree of growth retardation and no attempt has yet been made to dissociate the two and their effect on mental and behavioral development.
Effects of IUGR seem closely associated with accompanying factors; it is not always clear whether these should be treated as confounding factors and controlled for or not. Factors like socioeconomic status are clearly confounding factors, because they exist before and after IUGR occurs and are unlikely to be on the causal pathway between growth retardation and cognitive outcome. Asphyxia is a transient phenomenon and a factor that is likely to be on the causal pathway between IUGR and later outcomes. Where it is, at least partly, avoidable, it is of interest to know what specific outcomes, or what proportion of them, are attributable to asphyxia. If one wishes to assess the effect of IUGR in areas where factors like asphyxia are still less amenable to treatment, it seems more appropriate not to control for them.
Environmental circumstances can both enhance and reduce
developmental differences and other consequences. Mothers have been observed for
instance to react in a dichotomous way to the abnormal cries of malnourished
children, some devoting more time and attention to them, some less. Favorable
socio-economic conditions can have a protective effect, whereas under
unfavorable socioeconomic conditions, adverse effects can be amplified. The
general conclusion from Hack's review of the literature is that, while IUGR can
produce disadvantages in childhood that are significant, at least in statistical
terms, these tend to be most consistent and marked from the preschool years
through adolescence and gradually overridden by environmental influences in the
Among the commonly used indicators, a length deficit at an early age seems to be the best predictor of motor and mental development. Effects associated with ponderal index could be attributable mainly to length or height. Advocates of ponderal index argue that it provides the best reflection of the timing of the insult, and that this in turn could be of prognostic importance.