Normal Weight of Four- and Five-Month-Old Infants

As your child grows, it's important to know if he is healthy and growing as expected. Comparing your baby's weight to an expected weight is one way to ensure your child is growing well. Pediatricians use growth charts to accomplish this. For infants up until the age of 2, World Health Organization (WHO) growth charts are used to determine optimal growth for age.

How Infant Growth Charts Are Used

Growth charts are used by pediatricians during regular checkups to determine if your baby is growing normally, and to identify potential growth or nutrition-related problems. WHO growth charts are the standard by which infants can be compared because they are based on expected infant growth in ideal conditions, such as breastfeeding. In each of your baby's checkups, weight, length, head circumference and age will be plotted on the growth chart in order to compare and assess growth trends.

Interpreting Growth Charts

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The growth charts plot your infant's weight and other measurements onto age- and sex-matched growth curves. Normal weight in babies falls within a wide range on the WHO charts -- between the 2nd to 98th percentile. If your baby’s weight is plotted at the 70th percentile, for instance, this means she weighs more than 70 percent and less than 30 percent of infants her age and gender. Trends on the growth chart are also important, showing your baby's growth over time. If, for example, your baby is plotted at the 20th percentile, and over the months and years stays on this same curve, your infant's pediatrician may deem this normal and healthy. However, if at 5 months of age, your baby's weight drops down below the 2 percent growth curve, this may alert her pediatrician to investigate nutrition and health factors that may be negatively influencing growth.

Normal Weights Ranges

According to the 2006 WHO weight-for-age growth charts, the normal weight range for 4-month-old infants is defined as: - 12 lbs 6 oz to 18 lbs 15 oz for boys - 11 lbs 4 oz to 17 lbs 14 oz for girls

These same charts provide the following normal weight range for 5-month-old infants: - 13 lbs 7 oz to 20 lbs 5 oz for boys - 12 lbs 2 oz to 19 lbs 3 oz for girls


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Infant growth patterns are influenced by a variety of factors, including parental height, feeding practices, and the presence of health conditions or special health care needs, according to a study published in the February 2010 issue of "Pediatrics." In addition, if your baby was born prematurely -- at less than 37 weeks -- alternate growth charts will be used to determine whether your baby is growing at a healthy rate. Your baby's pediatrician can provide interpretation of the WHO charts as they relate to your baby's health, and address any concerns you have about your infant's growth and progress. .