A baby born prematurely (before 37 weeks of gestation) misses valuable time for development in the womb. Consequently, their physical and neurological maturity lags behind infants born at full term. Tracking progress solely by their birth date is an inaccurate measure of expected development. Healthcare professionals use adjusted age to provide a more accurate assessment of a preemie’s anticipated developmental timeline.
Understanding the Calculation
A premature baby operates with two different ages: chronological age and adjusted age. The chronological age is simply the time that has passed since the baby’s birth date, measured in days, weeks, or months. The adjusted age attempts to account for the time the infant spent outside the womb before reaching what would have been their full-term due date. This calculation provides a more realistic benchmark for developmental expectations.
The formula for calculating adjusted age is straightforward: take the child’s chronological age and subtract the number of weeks they were born prematurely. A full-term pregnancy is considered 40 weeks, so the difference between 40 weeks and the baby’s gestational age at birth determines how many weeks early they arrived. For example, if a child is six months old chronologically but was born two months (eight weeks) early, their adjusted age is four months.
This process effectively shifts the developmental starting line to the baby’s original due date, rather than their actual birth date. The adjusted age is the age against which a premature baby’s progress should be compared to a full-term infant’s milestone chart.
Applying Adjusted Age to Developmental Milestones
Adjusted age is primarily used by pediatricians and therapists to evaluate an infant’s progress across all areas of development, including gross motor, fine motor, cognitive, and language skills. By using the adjusted age, clinicians assess the child against the developmental expectations for a younger, full-term peer, giving them credit for the time they missed in utero.
For instance, a full-term baby typically begins to sit without support around six months of age. If a child is nine months old chronologically but was born three months early, their adjusted age is six months. In this scenario, the child would be expected to achieve the sitting milestone around their ninth chronological month, aligning perfectly with the six-month adjusted age benchmark. Similarly, the timing for first words, the pincer grasp, object permanence, and the eventual achievement of walking are all measured against this adjusted timeline.
If a preemie is not crawling at the chronological age of nine months, but their adjusted age is only seven months, they are still within the typical range for that milestone. This method ensures that the child’s care team can focus on actual developmental concerns rather than discrepancies caused by prematurity.
Transitioning Back to Chronological Age
Most healthcare providers stop using the adjusted age when the child reaches a chronological age of two years. By this point, the majority of premature infants have neurologically and physically “caught up” to their peers who were born at term. This transition marks the point where the child’s development is assessed purely by their birth date, aligning them with all other children.
In some cases, particularly for children born extremely prematurely, some specialists may continue to use the adjusted age for assessment up to three years of age. The decision to stop the adjustment is made on a case-by-case basis, depending on the child’s overall developmental trajectory and the degree of their initial prematurity.
Adjusted age is strictly for tracking developmental milestones. Chronological age must be used exclusively in specific medical and administrative situations. For example, medication dosages are always calculated based on the child’s chronological age and weight to ensure safety and effectiveness. Furthermore, official schedules for childhood vaccinations follow chronological age, as do legal requirements such as school enrollment cutoff dates.