Slow weight Gain

Definition

There are not universally-accepted criteria for slow weight gain or failure-to-thrive. Some suggest using one or more of the following indicators:

• Weight-for-age <3rd or <5th percentile
• Weight-for-length <3rd or <5th percentile
• Decreased weight gain velocity (weight-for-age falls more than 2 major percentiles over 3-6 months; for infants, some suggest using maximum weight percentile achieved between 4-8 weeks of age, not birthweight)
• Decrease of more than 2 standard deviations (weight-for-age or length-for-age) on growth chart over 3-6 month period

For young infants, however, these may not be appropriate due to the time required to observe trends. For example, growth problems in early infancy may have serious long-term consequences if not identified and corrected before 3-6 months of trend observation..

Care should be taken when interpreting growth data and identifying slow weight gain. For example, these two infants may be identified as having slow weight gain (based on the above criteria), but may actually be growing appropriately:

• An infant whose weight crosses percentile channels may have had inadequate in utero growth and may simply be demonstrating his genetic potential for growth. A complete assessment should include evaluation of in utero growth patterns.
• The corrected weight-for-age of an infant who was born prematurely is below the 5th percentile, but this infant's rate of weight gain is adequate. A complete assessment should include evaluation of growth velocity.

Sorting through these issues makes evaluation of slow weight gain in a young infant particularly difficult. It may be more helpful, then, to ask whether or not an infant’s growth pattern might be explained by one of the potential causes of slow weight gain.