His Weight Gain is Slowing Down

Patient Presentation

A 6-month-old male came to clinic for his health supervision visit. His parents had several questions about when he would start crawling and saying full words. They became more concerned when they saw the actual numbers of his weight gain since his 4 month appointment because they had had the sense that he was “slowing down” in his growth. He was breastfeeding every 4 hours for 20 minutes and they had started some cereal with iron in the past month. The past medical history showed a previously healthy, full-term infant with normal growth and development to date. The pertinent physical exam revealed an interactive infant who easily grabbed objects, sat by himself, said consonants and was rolling over. His vital signs were normal. His head circumference and length were consistently about 50%. His weight was slowly decreasing from the 50% at 2 months of age to between the 25%-50% currently. His examination was normal.

The diagnosis of a healthy male was made with normal growth and development. Although the resident had tried to educate the family that this was normal, the parents were still concerned when the attending physician came to see the infant. She reiterated what the resident had said and when showing the family the growth chart, pointed out the sharp vertical slope during the first 3 months of life, and how the growth curve slope changed over time. She said, “If your son keeps growing at the rate he was in the first few months of life, he is going to be Dad’s size when he is 2 years old.” She went on to say, “I know that seems kind of crazy, but I’ve actually done the calculations and its true, so he has to slow down how fast he’s growing.” She also discussed how in his case, the small, slow difference of being at the 25-50% currently was normal. “We’re also going to continue to watch how he grows and develops. If at any time you are concerned about his weight, just come back and we’ll re-weigh and measure him.” The parents seemed happy with the explanation, but afterwards the resident was skeptical about the growth rates. The attending and resident did a couple of sample calculations between seeing patients that day and the resident was then convinced about the growth rates.

Discussion
Since growth is such an important indicator of health in infants and children, parents are appropriately concerned that their children are growing well. A common concern for parents is that the child began at a certain percentile and is crossing growth percentiles but at a normal rate (i.e. moving toward their genetic potential). Some other parents believe that “fat babies” are healthy babies and want to see children growing at the top of the growth charts. Even if they do not believe in the “fat babies” idea, many families of children who are at the normal lower percentiles of the growth chart are worried that their child is not gaining enough weight. A careful review of the growth charts and parental education usually can assuage the concerns for most families.

Learning Point
Many parents will notice the normal changes in the growth rates of children particularly over the first 12 months of life, and will raise questions such as the parent above. Again careful review and explaining this normal phenomenon to parents in a way that they can comprehend usually helps the family to understand that their child is normal.

Newborn and young infants are growing at fantastic rates, almost so much that it is difficult to comprehend the rate. However if these infants were to continue growing at these rates, they would be too large much too soon. Therefore there must be a normal decrease in the growth rate such that the child continues to grow but more slowly. In the figure below, using a starting weight of 3.35 kg (50% for males) and the growth rate for an individual month, the predicted weight that a male infant would have attained was calculated at 2 and 5 years later. Weight gain was assumed to be compounded monthly.

Using the rate of weight gain between 2-3 months (= 14.5%), the infant would be around the size of an adult male by age 2 or 86.7 kg! This is obviously too great a weight gain for a normal infant. Using the weight gain rate at 6 months of age (=5.64%), the infant would be around 12.5 kg at 2 years of age, which is about the normal average weight of a male infant at that age (= 12.1 kg). And using the weight gain rates at 12 and 24 months of age, the infant would only be 6.1 kg and 5.0 kilograms at 2 years. Obviously this is too small a weight gain for a normal infant. Thus, one can see why there are normal decreases in weight gain rates particularly around 3 and 6 months of life. A growth chart is available to review here,

Not only is it imperative that the weight gain slow for the infant’s own health, but also for the mother. A breastfeeding mother would need to produce ~66,000 calories or ~940 liters of breastmilk to supply only the weight gain of the infant who was growing at the 3 month old rate over 2 years. This is about an additional 90 calories and 3 liters of fluid/day for the mother to consume that solely would be going toward the weight gain of the infant.

Questions for Further Discussion
1. How do the weight gain rates for premature infants compare to normal weight infants?
2. How do you determine mid-parental height? see How Do I Calculate Mid-Parental Height and Other Growth Parameters?

Related Cases

Disease: Child Development | Growth Disorders

Symptom/Presentation: Growth Problems | Health Maintenance and Disease Prevention

Specialty: General Pediatrics | Endocrinology | Nutrition / Dietetics

Age: Infant

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for these topics: Child Development and Growth Disorders.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Centers for Disease Control. Data Table for Boys Length-for-age and Weight-for-age Charts.
Available from the Internet at http://www.cdc.gov/growthcharts/who/boys_length_weight.htm (rev. 9/9/10, cited 4/30/14).

DePaul University, Quantitative Reasoning Center. Compound Interest Formula. Medscape.
Available from the Internet at https://qrc.depaul.edu/StudyGuide2009/Notes/Savings%20Accounts/Compound%20Interest.htm (rev. 2009, cited 4/30/14).

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