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To the Editor.—
In an article published in the March 2006 issue of Pediatrics, Bergvall et al1 show information to conclude that during early stages of gestation, growth in length and head circumference may be more important for intellectual development than weight increase. They arrive at this conclusion from a population-based cohort study conducted in 352125 boys in Sweden that showed that men who were born preterm with a very low birth weight for gestational age were not at increased risk for low intellectual performance, but those with a very short birth length or a very small head circumference for gestational age faced a nearly doubled risk for low intellectual performance compared with their appropriate peers.
We would like to add to this discussion the results of epidemiologic studies performed by our group, which show information about postnatal behavior linked to the period during pregnancy in which the deterioration in growth took place and also related to the etiologic factors implied in this growth retardation.
In an article published in 1982, intrauterine length and weight growth were shown to have different periods of major growth during pregnancy.2 The peak in the velocity of length growth is at 16 weeks of pregnancy, whereas weight increase shows its maximum value at 
33 weeks of pregnancy. As a consequence, at the end of the second trimester of pregnancy, length has reached 71% of the mean length at term, whereas weight is only 32% of the term infant weight. Consequently, 2 different patterns of intrauterine growth-restricted (IUGR) newborns can be distinguished: those with low height and weight and those with almost normal length and low weight, proportionate and disproportionate growth restriction, respectively. This pattern is related to the period of the growth restriction, and consequently, proportionate ones suffered a restriction all over pregnancy (chronic), whereas the disproportionate suffered growth restriction mainly in the third trimester of pregnancy (subacute).
The etiology of these 2 different types of growth restriction is different. The chronic types are related to maternal chronic malnutrition, smoking from early pregnancy, genetic factors, and maternal vascular diseases. Main causes associated with fetal growth restriction during the third trimester of pregnancy are pregnancy-induced hypertension, preeclampsia-eclampsia, and relatively well-nourished women with low weight gain during pregnancy.2
Follow-up studies evaluating intellectual performance of these different groups of newborns showed that those with chronic intrauterine growth restriction showed significantly poor performance.3–5
In conclusion, we wish to add to the contribution of this article that the association found with intellectual performance and fetal length restriction could be linked to the period during pregnancy in which such growth was restricted and to the etiology associated with such restriction.
Finally, we would like to mention that these findings are of great concern for developing countries. These countries have a great proportion of children born with growth restriction. In addition, we have shown that populations in developing countries have a higher incidence of chronically malnourished neonates (proportionate growth restriction) within their IUGR population (67%–79% of the IUGR population), whereas populations in developed countries have a predominance of subacute fetal malnutrition, with the proportion of chronically malnourished newborns being only 20% to 40% of the total IUGR population.6
REFERENCES
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