Growth Charts for Premature Babies: Following Their Own Curve

One thing all parents have in common is worrying about their baby’s growth and development. Parents often ask “Is my child on a good percentile?”

Every baby should be monitored for growth, and it is important to use the right tool to do so. Growth charts are standards to identify how children should grow over time. However, there are different versions available to give the parent and medical professional guidance. Understanding different types of growth charts can help ease a parent’s mind.

Term Infant Growth Charts

The Center of Disease Control (CDC) and the World Health Organization (WHO) recommend using WHO growth charts to monitor growth for full-term infants from 0-2 years of age. The American College of Obstetricians and Gynecologists (ACOG) define a term infant as born between 37-40 weeks gestation.

WHO growth charts:

• Use breastfed infants as the norm for growth. Chart patterns reflect infants breastfed for at least 4 months and still breastfeeding at 12 months.
• Describe how infants should grow under optimal conditions.
• Are gender-specific.
• Include Weight, Length, Head Circumference and Weight-for-Length in monthly increments.
• Have percentile curves for each chart, as follows:2^nd, 5^th, 10^th, 25^th, 50^th, 75^th, 90^th, 95^th and 98^th.
• Do not recommended using Body Mass Index (BMI) in children under 2 years of age.

Preterm Infant Growth Charts

ACOG defines a preterm infant as born at less than 37 weeks gestational age. Preterm growth charts should be used for these babies. Preterm growth charts aim to mimic growth that occurs during a term pregnancy. The Fenton preterm growth chart is used by many medical professionals.   

Fenton growth charts:

• Are based on birth size of over 4 million infants with confirmed gestational ages in developed countries including Germany, Italy, United States, Austria, Scotland and Canada.
• Begin at 22 weeks and end at 50 weeks.
• Should be used in conjunction with term charts after 40 weeks.
• Are gender-specific.
• Include Weight, Length and Head Circumference in weekly increments.
• Do not include Weight-for-Length or BMI.
• Include percentiles, as follows: 3^rd, 10^th, 50^th, 90^th and 97^th.

Plotting the Former Preterm Infant on Term Growth Charts 

WHO growth charts should be used for preterm infants who are corrected to term age. Corrected age is used to describe the child’s age from the original due date.

• When plotting a baby’s growth, it is recommended to use corrected age through 2 years from the original due date. Some experts recommend correcting through 3 years.
• If age is not corrected, the infant may appear to be growing suboptimally.
• Catch-up growth can occur during this 2 year period.
• Catch-up growth here refers to rapid growth of preterm infants that minimizes the size difference with term counterparts.
• Using corrected age during a period of catch-up growth provides the infant time to achieve typical growth standards.
• Rate of catch-up growth is affected by birth weight, gestational age at birth, genetic potential and medical condition.

It’s important to remember there are generally no good or bad individual percentiles. Weight, length and head circumference are looked at together for an overall picture. Plotting growth on  multiple points over time is also important. It is difficult to assess growth with only a few measurements in a short period of time.

Ideally a child will plot on the growth chart (not above or below) and continue to follow a fairly consistent and proportional (weight similar to length) trend. A medical professional will work with each parent to assess growth and, if needed, create an individualized plan.