Limitations of available evidence

Several factors hamper the interpretation of the empirical evidence relating intrauterine growth retardation (IUGR), both in infants born at term and preterm, to neurological, sensory, cognitive and behavioral function:

- The definitions of both IUGR and putative outcomes vary.

- Study samples are heterogeneous with respect to the etiology of IUGR, and one therefore cannot tell if outcomes differ as a function of the causes that led to IUGR.

- IUGR is almost always associated with other conditions having an adverse effect on outcomes. Pregnancy and neonatal complications, especially those associated with hypoxia, as well as postnatal malnutrition and childhood illness, are frequently associated with IUGR and may further aggravate the effect of IUGR. Some mediating and modifying factors, such as socioeconomic and environmental deprivation, are likely to persist and to have a continuing effect throughout the life span.

- The majority of studies have been conducted in high income countries and in the pre-intensive-care era.

- In follow-up studies of older children the control of postnatal influences and biased sample attrition become major problems.