Measuring Growth

Babies born now with cystic fibrosis will benefit from all the new knowledge gained from research. Research shows that good nutrition will help your child be their best. Because of this, the CF team is very attentive to supporting optimal growth. Height and weight measurements are part of every clinic visit and this is just the beginning: there are several ways that we assess growth.

Children 0 to 23 Months

For ages 0-23 months, we use the standard growth chart and plot weight against length to see how thin or heavy your baby is. An ideal weight for length is greater than or equal to the 50th percentile. Find links to growth charts at the bottom of this page.

Body Mass Index: Ages 2 Years & Older

Body mass index (BMI) is calculated from height and weight and then converted to a percentile using the growth chart. BMI tells you how thin or heavy you are, and it is widely used in general healthcare. Calculate BMI on the Centers for Disease Control and Prevention website.

Using the "BMI-for-age" standard growth, plot the BMI against the child's age to determine the "BMI percentile."

For children with CF ages 2-20 years, having a BMI greater than or equal to the 50th percentile for age is ideal. For adults with CF, percentiles are not used. Instead, the goal for men is a BMI of 23 or more, and for women it is a BMI of 22 or more.

Genetic Potential for Height

Genetic potential is a very helpful tool. We start with the parents’ heights. This allows us to calculate the child’s genetic potential which is a range of heights that is reasonable to achieve based on the parents’ heights. A sample calculation is below.

Step 1: Find the target height (using inches).
  • For boys: (Add mother's height plus five) plus the father's height and divide by two.
  • For girls: (Subtract five from the father's height), add the mother's height and divide by two.
Step 2:  Calculate the target height range.
  • Upper end of range: To the target height, add 3.5 inches for girls, and 4 inches for boys.
  • Lower end of range: From the target height, subtract 3.5 inches for girls and 4 inches for boys.

Step 3: Using a stature growth chart for 2-20 year olds, plot the target height at age 20, and also plot the upper and lower end of the range.

The percentiles that correspond to the upper and lower points define the genetic potential.

Example: A boy’s mother is 5 feet 4 inches tall and his father is 5 feet 9 inches tall. Find the target height = (64 inches + 5) + 69 inches, then divided by 2  = 69 inches

Find the Range

  • 69 inches + 4 inches = 73 inches (this is the upper range)
  • 69 inches – 4 inches = 65 inches  (this is the lower range)

Plotting these on the growth chart shows that the target height is at roughly at the 40th percentile. The upper range is at roughly the 88th percentile, and the lower range is at roughly the 5th percentile.

The boy’s genetic potential is between the 5th percentile and 88th percentile. The goal is to have this boy’s height continue to fall at or above the 5th percentile as he grows older.

Monitoring the Growth Rate

One of the benefits of regular visits with the CF team is that growth can be closely monitored. Weight loss or the lack of optimal weight and height gains can be recognized early. After every visit, you will receive the “After Visit Summary” that includes the height, weight and weight for length percentile. In addition you may request a copy of the growth chart from the visit.