by Alan Greene, MD, FAAP
When I see a new baby in my office for her first visit, her parents often get more excited about finding out their child's weight than just about anything else. The scale becomes the focus of the visit. "Is my baby growing okay?" is an urgent question for parents until they are sure of the answer. This deeply rooted concern makes sense.
Growth is central to childhood. In fact, an organism is considered "a child" during that period of its life in which it is growing.
Growth is particularly noticeable and rapid during the beginnings of life. In the first four to six months, a baby typically doubles her birth weight. She will triple her birth weight by the time she is a year old. Maximal brain growth also occurs during the first six months of life. The brain grows as much during a child's first year as it will during the entire rest of her life.
A child is failing to thrive when she is not growing at the expected rate for her age, or if her weight is disproportionately low compared to her height and head circumference.
A simplistic but very useful way to look at growth failure is to consider that in order to grow, a child must take in adequate calories, absorb those calories, and use them for growth.
If a child is not growing well, first consider whether she is actually taking in an adequate number of calories (and other nutrients). What is she being fed? How much is offered and how often? How much does she actually take? Is she able to suck and swallow adequately? Most cases of failure to thrive in infants can be solved by carefully addressing these questions.
If caloric and other nutrient intake is adequate, consider whether the calories are continuing down the gastrointestinal tract, being digested, and being absorbed into the body. Sometimes the food is vomited back up either due to a blockage in the gastrointestinal tract or a condition called gastroesophageal reflux, in which food travels backwards from the stomach to the esophagus.
Sometimes the calories make it through the stomach, but are not absorbed -- they are lost out the other end -- either because of diarrhea or because of an inability to absorb the nutrients. Possible underlying causes for this include viral, bacterial, or parasitic infection, a digestive enzyme deficiency, a genetic disease (such as cystic fibrosis), or a milk protein intolerance.
When adequate calories are consumed and absorbed into the body, the calories could be spilling out in the urine if the kidneys are not effective at holding in the protein. If the fuel remains safely in the body, the body could still be burning it at a faster-than-normal rate, leaving insufficient calories for growth. Possible causes of this hyper-metabolic state include hyperthyroidism, chronic infection, congenital heart disease, or malignancy.
Some children will even fail to thrive in the face of adequate calorie absorption simply from extreme neglect. Kids who are not hugged, held, and cared for don't grow. This has been clearly demonstrated in orphanages where the adult-child ratio is very low. Even if these children are being well nourished, they often fail to thrive, simply because they lack personal care.
So, as you can see, growth requires the smooth working together of many systems throughout the body. The specific causes of failure to thrive are quite numerous, with problems in every major organ system represented. The most common causes for failure to thrive vary with age. In the first three months of life feeding difficulties, infections, gastroesophageal reflux, inborn errors of metabolism, cystic fibrosis, and milk-protein intolerance top the list. Simply switching to formula is not a sufficient solution if your child doesn't respond with steady growth.
Many infants regain their birth weights by one week of age. Most regain their birth weights by two weeks of age and have a steady weight gain thereafter. A child who has gone seven weeks without regaining her birth weight deserves a thorough work-up to determine the cause. This work-up should begin with a detailed feeding history and a careful physical examination. If the cause for failure to thrive is not apparent, the next step would be to run some simple screening lab tests including a Complete Blood Count (CBC) with differential, urinalysis, and a measurement of serum electrolytes, BUN and creatinine.