5. The CDC Growth Chart Reference Population

Other Characteristics of the Reference Population

Following Kessler and Dawson (1999), calculate a very low birth weight infant's gestation-adjusted age as follows:

Determine the infant's gestational age in weeks. [Ultrasonographic examination provides a more accurate measure of gestational age than post-natal assessments (Alexander et al., 1992).]

Subtract the child's gestational age in weeks from 40 weeks (gestational age of term infant) to determine the adjustment for prematurity in weeks.

Subtract the adjustment for prematurity in weeks from the child's post-natal age in weeks to determine the child's gestation-adjusted age.

 EXAMPLE Randy was born prematurely on March 19, 2001. His gestational age at birth was determined to be 30 weeks based on ultrasonographic examination. At the time of the June 11, 2001, clinic visit, his postnatal age is 12 weeks. What is his gestation-adjusted age? 30 = gestational age in weeks 40 - 30 = 10 weeks adjustment for prematurity 12 - 10 = 2 weeks gestation-adjusted age If this were plotted on a growth chart, anthropometric measurements would be plotted for a 2 week old infant.