Q: The doctor was worried that my neighbor’s 2-week-old son was not gaining enough weight and was not “thriving.” What does this mean?

Q: The doctor was worried that my neighbor’s 2-week-old son was not gaining enough weight and was not “thriving.” What does this mean?

A: Birth weight, length and head circumference vary a lot from one newborn to another; however, all newborns’ “jobs” are the same: to eat, sleep and excrete so they can grow.

A newborn’s progress is gauged by plotting their weight, length and head circumference on a graph as they age. This is done at the regular newborn visits, and there are different “standard curves” defining what percentile measurements are expected for girls/boys, full-term/premature, Down syndrome (and some other genetic conditions), heritage/race and other variables.

The 50th percentile is the expected average measurement for a child of the same age/sex/race/genetic condition etc., and the 10th percentile means 90 percent of comparable kids would be larger.

Almost all newborns lose weight after birth, typically about 5 percent of their weight (slightly more in breastfed babies). This is considered normal, and they typically regain their birth weight by two weeks of age.

For newborns, a loss of more than 10 percent of their birth weight or failure to regain their birth weight by 2 weeks of age may be a clue that they are not growing as expected. Other possible indications of newborn failure to thrive, include being below the 5th percentile or ‘crossing’ at least two major percentiles –– for example, being in the 30th percentile at a certain age and then dropping to the 20th, and then 10th percentiles on subsequent follow ups).

Note that the above criteria indicate a need to evaluate for possible problems, but many infants who meet one of these criteria subsequently start to gain weight and grow along the percentile curve appropriate for them. In fact, up to a quarter of all children shift to lower percentile curves within the first two years of their lives.

When children are failing to thrive, it is because they are not getting adequate usable nutrition. This can be because they do not have adequate nutritional intake; they are not able to absorb/utilize enough nutrition despite getting adequate intake; or because their nutritional needs are higher than their intake can keep up with. Differentiating between these and identifying the underlying cause is the goal of a failure-to-thrive evaluation.

Causes of inadequate nutritional intake include:

Limited nutrition availability. For example, from insufficient maternal lactation (for breastfed infants), inadequate nutritional offering due to caregiver poverty or caregiver psychosocial issues, such as depression.

Limited infant suckle. For example, due to swallowing dysfunction or anatomic issues, such as cleft palate.

Inadequate nutritional absorption may be due to:

Gastrointestinal conditions. For example, liver disease, intestinal conditions, intestinal infections, cystic fibrosis and others.

Severe vomiting or diarrhea, from many causes.

Food allergies or intolerances.

Increased nutrient requirements can come from:

Many different chronic diseases. For example, certain inflammatory conditions.

Certain infections.

Certain cancers.

Some hormonal conditions. For example, thyroid conditions.

Certain breathing or heart conditions.

Failure to thrive, or FTT, evaluation begins with a complete history and physical examination:

Identification of a genetic condition may lead to use of a more appropriate growth chart, obviating the FTT diagnosis.

Breathing problems, elevated heart rate or heart murmurs and other findings may give clues that the baby’s metabolic needs are elevated.

Evaluation of the baby’s urination and bowel movement characteristics may give clues to possible poor nutritional absorption.

Evaluation of what the baby has been eating, how frequently and how much they take during each feeding is important to estimate their nutritional intake.

Suspicious findings may indicate the need for further testing, such as certain blood tests.

Treatment of FTT includes increasing nutritional offering as well as specific treatment(s) for any underlying identified condition. The infant will need to be closely monitored to ensure they begin to adequately grow. For severe cases, hospitalization for more aggressive evaluation and/or treatment may be needed.

FTT may lead to short stature, delay in neurological development and possibly subsequent behavioral issues. Depending on the underlying cause of the FTT, these problems can be minimized by early detection and early initiation of treatment. This is one of the many reasons that regular well baby visits are so important.

Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.