Adjusted Age Calculator - Preterm Babies Corrected Age

Adjusted Age for Premature Babies

If a baby has been born early, the corrected or developmental age will need to be accounted for, in parallel with the chronological age from birth, for a period of time, up to 24-36 months. A premature baby might experience developmental milestones at different times from a full-term baby, usually to their corrected age.

A premature baby born at 32 weeks gestational age will require a further 8 weeks of growth before their brain neurological system start to function similarly to those of a newborn. So, the corrected age allows an accurate assessment of their developmental abilities.

Studies have shown that corrected age is even the more relevant when it comes to the development of motor skills compared to cognitive skills, with premature babies being found to score significantly lower on motor skills than on mental skills in the first 12 months of life.

The chronological age is the number of years, months, weeks and days from the actual birth while the corrected age is calculated by subtracting the weeks of prematurity from the chronological age. This is also known as adjusted age or post conceptual age.

• Corrected age = Chronological age – Weeks of prematurity*

* Where weeks of prematurity = 40 weeks – gestational age at birth

Returning to the example of a premature baby born at 32 weeks, when their chronological age will be of 4 months, their corrected and developmental age will be of 2 months.

Prematurity is a notable risk factor in a child’s development so close monitoring will take place, with professionals referring to both the chronological and adjusted age.

Estimating Catch-up Period

Many professionals use both the chronological and corrected age until the infant reaches 24 – 36 months, a time at which is it considered that generally, the most premature infants have caught up and they are reaching developmental milestones similarly to infants born at term.

There is however, a formula that may be used to estimate for how long the corrected age may be used. The prematurity weeks are multiplied by 10 to give the number of weeks needed to correct the development gap from prematurity.

• Catch up period (weeks) = Prematurity weeks x 10

For example, in the case of a premature baby born 8 weeks early, it is estimated they would require 80 weeks (1 year and 7 months) to catch up.

Ouden et al. found that in the first 12 months of life:

• 80-99% of premature infants achieved positive scores on age-specific developmental tasks (with corrected age);
• only 30-80% achieved positive scores when chronological ages were used.

At 24 months, 90% of premature infants scored similarly to at term babies at developmental tasks.

References

Girsen AI, Do SC, El-Sayed YY, Hintz SR, Blumenfeld YJ. Association between small-for-gestational age and neurocognitive impairment at two years of corrected age among infants born at preterm gestational ages: a cohort study. J Perinatol. 2017; 37(8):958-962.

Chau V, Synnes A, Grunau RE, Poskitt KJ, Brant R, Miller SP. Abnormal brain maturation in preterm neonates associated with adverse developmental outcomes. Neurology. 2013; 81(24):2082-9.

Wilcox AJ, Weinberg CR, Basso O. On the pitfalls of adjusting for gestational age at birth. Am J Epidemiol. 2011; 174(9):1062-8.

Romeo DM, Di Stefano A, Conversano M, et al. Neurodevelopmental outcome at 12 and 18 months in late preterm infants. Eur J Paediatr Neurol. 2010; 14(6):503-507.

Den Ouden L, Rijken M, Brand R, Verloove-Vanhorick SP, Ruys JH. Is it correct to correct? Developmental milestones in 555 "normal" preterm infants compared with term infants. J Pediatr. 1991; 118(3):399-404.