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Comments on studies

Most studies only looked at children at one narrow age range. However, cognitive deficits appear to change over time and the findings depend on the age at follow-up. Looking longitudinally at the studies, differences were less likely to be found in the first year of life but tended to be present between two and three years of age. After that differences were smaller and sometimes did not reach significant levels. A good example of this is in the Guatemalan studies (Villar et al, 1984; Gorman and Pollitt, 1992) where differences were not present in the first 15 months, then appeared between 24 and 36 months, but were not significant at 4 and 5 years. Thus it is clear, even from these limited data, that longitudinal studies are essential if we are to understand the developmental progress of SGA children.

Many of the studies after three years, showed that deficits in cognition were only found in the highest risk children such as the smallest, or ones with early IUGR. It is possible that the cut-off of the 10th centile for the definition of SGA is too high to define risk of poor cognition.

Low income countries

There were only two studies of SGA term babies from low income countries where the problem is largest and the aetiology may be different. This is insufficient to draw any conclusions. Following birth, these children are exposed to poor nutrition and a high level of infections as well as other conditions of poverty. SGA babies' development appears to be more vulnerable to a hostile environment. Thus, the children's long term development is dependent to a large extent on the quality of their environment and their nutrition and health in childhood, therefore surprising that the Guatemalan study (Gorman and Pollitt, 1992) found no significant differences at 5 and 6 years of age. They used the 10th centile to define SGA and this may be an explanation.

Table 3. Studies of term, SGA children aged 2-6 years

* SGA infants had significantly lower scores than NBW infants
ns = not significantly different

Figure 3. McCarthy general cognitive index at 5 years of age according to timing of intrauterine growth retardation (Harvey et al, 1982)

Size at birth

A few studies compared API with LPI children and the findings were inconsistent. The API children were found to have poorer development in one study (Villar et al, 1984) but the differences were not significant in two others (Tenovuo et al, 1988; Nelson et al, 1996; Goldenberg et al, in press).

Social background

Relatively few investigators had comprehensive measures of both the macro and micro-environment and took them into account in the analysis. When investigators had comprehensive measures of social background they have tended to control for them rather than looking for interactions between them and birth weight. However, interactions were reported in several studies (Nelson et al, 1996; Harvey et al, 1982; Pryor, 1992; Grantham-McGregor et al, submitted).

Outcome measurements

It is important to assess a range of behaviours. However most investigators have used only one measure of cognition and sometimes a neurological examination (reported by Goldenberg at this workshop). This has often been an infant developmental scale in the under twos and an IQ test in the older children. There has been little attempt to look at social and emotional development, which are critically important for the child's future success in life. Where behaviour was examined differences were usually found.

Implications

There is a need to re-examine the definition of SGA in terms of the risk for poor cognitive development. The 10th centile for gestational age may be too high. There is also a need for good, longitudinal studies in developing countries which have a comprehensive range of developmental measures including social and emotional development. In addition, interactions between SGA and health, nutrition and the environment need to be examined more carefully.

References

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Bradley RH & Caldwell BM (1984): Children: A study of the relationship between home environment and cognitive development during the first 5 years. In: AW. Gottffied (ed.): Home environment and early cognitive development. Academic Press Inc., pp. 5-56.

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Drillien CM, Thomson AJM & Burgoyne K (1980): Low-birthweight children at early school-age: A longitudinal study. Dev. Med. Child Neurol. 22, 26-47

Fancourt R. Campbell S. Harvey D & Norman AP (1976): Follow-up study of small-for-dates babies. BMJ 1, 1435-1437.

Fitzhardinge PM & Steven EM (1972): The small-for-date infant II. Neurological and intellectual sequelae. Pediatrics 50, 50-57.

Goldenberg RL et al: Pregnancy outcome and intelligence at age five. Am. J. Obstet. Gynecol. (in press).

Goldenberg RL, Davis R. Cutter et al (1989): Prematurity, postdate and growth retardation: The influence of ultrasonography on reported gestational age. Am. J. Obstet. Gynecol. 160, 462-470.

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Grantham-McGregor SM, Lira PIC, Ashworth A, Morris SS & Assuncao MAS: The development of low birthweight term infants and the effects of the environment in north-east Brazil. J. Pediatr. (in press).

Hadders-Algra M, Huisjes HJ & Touwen BCL (1988): Preterm or small for-gestation-age infants. Neurological and behavioural development at the age of 6 years. Eur. J. Pediatr. 147, 460-467.

Harvey D, Prince J, Bunton J, Parkinson C & Campbell S (1982): Abilities of children who were small-for-gestational-age babies. Pediatrics 69, 296-300.

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Horowitz ED (1989): Using developmental theory to guide the search for the effects of biological risk factors on the development of children. Am. J. Clin. Nutr. 50, 589-597.

Kramer MS, Olivier M, Mclean FH, Willis DM & Usher RH (1990): Impact of intrauterine growth retardation and body proportionality on fetal and neonatal outcome. Pediatrics 86, 707-713.

Low JA, Gailbraith RS, Muir D, Killen H. Karchmar J & Campbell D (1978): Intrauterine growth retardation: A preliminary report of long term morbidity. Am. J. Obstet. Gynecol. 130, 534-545.

Low JA, Galbraith RS, Muir DW, Broekhoven LH, Wilkinson JEW & Karchmar EJ (1985): The contribution of fetal-newborn complications to motor and cognitive deficits. Dev. Med. Child Neurol. 27, 578-587.

Nelson KG, Goldenberg RL, Hoffman H & Cliver S (1996): Growth and development during the first year in a cohort of low income term-born American children. In press.

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Pryor JE (1992): Physical and developmental status of preschool small-for gestation-age children: A comparative study. J. Paediatr. Child Health 28, 162-167.

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Tenovuo A, Kero P, Korvenranta H, Piekkala P, Sillanpaa M & Erkkola R (1988): Developmental outcome of 519 small-for-gestational age children at the age of two years. Hippokrates Verlag GmbH 19, 41-45.

Villar J & Belizan JM (1982): The relative contribution of prematurity and fetal growth retardation to low birth weight in developing and developed societies. Am. J. Obstet. Gynecol. 143, 793-798.

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Discussion

It is very difficult to isolate the effects of IUGR. At this stage, studies that have found lower average IQ levels in formerly IUGR children do not allow the segregation of effects into those that are due to IUGR per se and those reflecting the fact that IUGR children are more likely to be born into disadvantaged families. Another explanation for developmental delays in IUGR babies, regardless of the environment they are born into, may be that caretakers treat them more in accordance with their size (i.e., as if they were younger) than in accordance with their age. If a small child is considered particularly vulnerable and therefore protected, this may be an advantage in the short but a disadvantage in the long term.

Length early in life seems to be the best predictor of mental development and effects associated with ponderal index could be attributable mainly to length. Some discussants, however, argue that ponderal indexes give a clearer indication of the timing of the growth-retarding insult, which could have prognostic importance.

When tests, developed in industrialized countries are used in developing countries, the question of culture specificity has to be addressed. A study was undertaken to assess what Guatemalans meant by intelligence in their children, and ratings according, to these criteria correlated quite well with results the same children achieved on adapted versions of more commonly used intelligence scales.

Mental test scores not only reflect intelligence, but also attention span and motivation. Even though undernourished young children have been described as suffering from attention deficit, no information is available on possible socio-emotional effects of IUGR.

Another question is what a difference of a few points in a test score means in terms of the ability of people to cope with problems they actually encounter in their lives. Several discussants therefore recommend the inclusion of direct measures of economic success, such as educational attainment, occupation, work productivity, income and wealth, in studies of long-term outcomes.

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