Chronological age is your baby's age based on his or her birthday. This is the age we normally use in conversation, and the age that will one day go on your child's school forms, driver's license, etc. It's perfectly normal to use chronological age when talking to friends and family about your child, when filling out paperwork, and so on.
But chronological age can be misleading. If your baby was born months ahead of schedule, he or she did not have time to finish developing in the womb. Premature babies are usually smaller than full-term babies, and they develop more slowly. It can be difficult to judge whether a premature baby is growing properly. For example, a baby born at 26 weeks is not as developed as a baby born at 40 weeks. Even if those two babies share a birthday, they will not grow and develop at the same rate. The premature baby may take much longer to sit upright or gain weight than the baby born at 40 weeks, even if both are healthy babies and growing at the right rate. Health care providers should be aware that an infant was born prematurely before giving advice based on the infant's growth and development.
Corrected age (CA) is based on the age the infant would be if he or she had been born on the original due date. If a baby should have been born on June 1st, his corrected age on September 1st will be 3 months old, even if he was born in April. Corrected age is not useful for a baby born only a few days or weeks early, because those babies are born near to full development. Corrected age is also called gestationally corrected age.
To calculate your baby's corrected age:
- Start with his chronological age based on his birthday.
- Figure out how many weeks or months early your baby arrived.
- Use this formula:
(chronological age in weeks/months) – (# weeks/months premature) = corrected age
So, if your baby was born 8 months ago today, but she was 2 months early, her corrected age would be 8 minus 2 months, or 6 months.
No matter which age you use, your baby's birthday will always be the day on which you gave birth. There's no set time to stop using corrected age and start using chronological age. Most health care providers use corrected age for the first two years. It may be a good idea to make the switch when the child starts school, since schools use age based on the child's birthday. It may also be a good idea to explain your child's age to the school counselor, so that the school can measure your child's test results correctly.
January 2007
