Infants whose weight gain after birth is particularly slow are traditionally identified in pediatric medicine as “failing to thrive.”
Two key methodological criteria are important in considering any research on this condition: whether slow weight gain after birth has been clearly distinguished from slow weight gain before birth, since these have quite different determinants; and whether the sample studied is representative – in particular whether it comes from the screening of a whole population or from a source in which the condition has already been clinically identified, with associated selection bias.
Studies dealing with the causes of slow weight gain in infancy have often not met these methodological criteria. There is some evidence that there are different patterns of mother–infant interaction among clinically identified groups of children identified as failing to thrive, and that they have different patterns of attachment, but there is little or no evidence that these differences account for the development of the condition or even precede its development. There is evidence from mothers’ reports that infants who fail thrive are more difficult to feed, and some evidence from direct observation to support this.
Studies dealing with the consequences of slow weight gain, many of which are of better quality, provide evidence that failure to thrive is associated with poorer intellectual development. Summarized over the studies with the most representative samples, the effect is quite small (3 or 4 IQ points). More recent evidence from a large birth cohort study shows that this is actually a component of a much more general relationship between weight gain in infancy and later measured intelligence, and that the key period over which weight gain matters is the 2 months immediately after birth.
Weight Gain Child Interaction Maternal Behavior Insecure Attachment Intellectual Development
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Avon Longitudinal Study of Parents and Children
Body mass index
Failure to thrive
Standard deviation (standard deviation score)
Wechsler Intelligence Scale for Children
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