A birth is considered premature if it occurs before the 37th week of pregnancy. Babies born early have less time to develop in the womb, meaning their bodies and brains may not be as mature as those of a full-term infant. Because of this developmental gap, pediatricians and parents use a specialized calculation to track a premature baby’s progress. This adjusted age helps accurately measure growth and development against their level of maturity, rather than simply the time since their birth. Understanding this calculation is important for setting appropriate expectations for a preemie’s first few years of life.
Understanding the Two Ages: Chronological and Corrected
A premature baby effectively has two different ages that are tracked during early childhood. The first is the Chronological Age, which is the exact time that has passed since the baby’s date of birth. This age is used for standard record-keeping, such as celebrating birthdays, and is the age most people would reference.
The second, more important measure for developmental tracking, is the Corrected Age, also called the Adjusted Age. This age reflects the time the baby would have spent developing in the womb if the pregnancy had reached full term. It is calculated by taking the baby’s chronological age and subtracting the amount of time they were born early, providing a realistic developmental baseline.
The Step-by-Step Calculation Method
Calculating a premature baby’s corrected age involves a straightforward three-step subtraction process, which is easiest to perform in weeks. The first step is to determine how many weeks premature the baby was at birth by subtracting the baby’s gestational age at birth from 40 weeks, the standard length used for a full-term pregnancy.
The second step is to determine the baby’s current chronological age in weeks, counting the time elapsed from the date of birth until the present day. Finally, the number of weeks the baby was premature is subtracted from the current chronological age. The resulting number is the baby’s corrected age, which reflects their true developmental age.
For example, consider a baby born at 32 weeks’ gestation who is now 24 weeks old chronologically. First, determine the prematurity: 40 weeks minus 32 weeks equals 8 weeks premature. Next, subtract those 8 weeks from the current chronological age: 24 weeks minus 8 weeks equals a corrected age of 16 weeks.
In another scenario, imagine a baby born at 30 weeks’ gestation who is now six months old chronologically (approximately 26 weeks). This baby was 10 weeks premature (40 weeks minus 30 weeks). Subtracting the 10 weeks of prematurity from the 26 chronological weeks results in a corrected age of 16 weeks, or four months.
Applying Corrected Age to Developmental Milestones
The corrected age is the standard measure used by pediatricians and other healthcare providers to evaluate a preemie’s developmental progress. Milestones such as rolling over, sitting up, or crawling are based on averages for full-term infants. Using the corrected age allows parents and doctors to track whether the baby is meeting these milestones at a pace appropriate for their level of maturity.
The corrected age is typically used for tracking development until the child reaches about two years old. By this age, most premature children have demonstrated “catch-up growth,” aligning their skills and size more closely with their peers who were born full-term. Parents should maintain open communication with their pediatrician regarding any concerns about milestone achievement. Early intervention services may be recommended if a child is not meeting milestones even when using the corrected age as a guide.