As part of regular well-child care, the doctor calculates your child's body mass index (BMI) and determines where it falls on the national BMI-for-age growth chart. The BMI indicates if your child is overweight for his or her age and height.Using the growth chart, your doctor determines your child's percentile, meaning how your child compares to other children of the same sex and age. So, for example, you might be told that your child is in the 80th percentile. This means that compared with other children of the same sex and age, 80 percent have a lower BMI.Cutoff points on these growth charts, established by the Centers for Disease Control and Prevention (CDC), help identify overweight children:

• BMI-for-age between 85th and 95th percentiles - at risk of overweight

• BMI-for-age over 95th percentile -overweight

Because BMI doesn't consider things like being muscular or having a larger-than-average body frame and because growth patterns vary greatly among children, your doctor also factors your child's growth and development into the overall weight assessment. This helps determine whether your child's weight is a health concern.

In addition to BMI and charting weight on the growth charts, the doctor also evaluates:

• Your family's history of obesity and weight-related health problems, such as diabetes.

• Your child's eating habits and calorie intake.

• Your child's activity level

• Other health conditions your child may have.

Diagnosis

A child's weight is evaluated by his or her primary care pediatrician during regular check-ups and office visits. Weight issues rarely sprout rapidly but rather develop over time. If you think your child has a weight problem, make an appointment with his or her pediatrician or primary care doctor.

There are two main tools doctors use to assess a child's weight:

• Growth Charts

These charts are used throughout a child's development to assess growth, both height and weight, as compared to other children the same age and to watch how a child's body changes over time. Almost every doctor uses the same growth charts from the Centers for Disease Control and Prevention (CDC), based on the measurements of thousands of children.

• Body Mass Index (BMI) for Age Charts

This index uses height, weight, gender and age to assess a child's weight. A formula is used to calculate a child's BMI:

BMI = weight in kilograms / (height in meters) ²

The number is plotted on a growth chart -- greater than the 95 percentile is considered overweight or obese. A child who falls between the 85 percentile and 95 percentile is considered at risk for becoming overweight.

Note that this is higher than the cutoffs for adults. An adult with a BMI between 25 and 30 is considered overweight, while an adult with a BMI over 30 is considered obese.

If you have questions about your child's weight, ask to see his or her growth chart. It can be helpful to look at your child's measurements over time. Children also may like to see their chart.

If your child is overweight or at risk, your doctor or a nutritionist may do a 24-hour food recall with you and your child. This is a tool for gathering information about meal patterns, the consumption of sugared-beverages and snacking routines. You and your child may be asked about his or her level of physical activity.

Children determined to be overweight or at risk should be referred by their pediatrician to a registered dietitian and possibly a comprehensive obesity program, such as the UCSF Weight Assessment for Teen and Child Health (WATCH) Clinic.