Why use it

Judging a preterm child against chronological age overestimates delay: an infant born at 28 weeks is 12 weeks "younger" developmentally than the calendar suggests. Using corrected age avoids false alarms, while stopping the correction at the published age avoids masking a real delay later.

About

Corrected age is the chronological age (time since birth) minus the number of weeks the child was born before 40 weeks of gestation. For a child born preterm (before 37 completed weeks), developmental milestones and growth are interpreted against corrected age during the first years of life; in the words of the AAP, "during the first 2 years, using your baby's corrected age will give you a better idea when he or she should reach common developmental goals". The Brazilian Ministry of Health Caderneta da Criança (2025) states that corrected age is used until 2 years of chronological age, and until 3 years when gestational age at birth was under 28 weeks. The AAP (HealthyChildren.org) and the Portuguese national child health programme (DGS, PNSIJ 2013) also describe correction over the first 2 years.

When to use

Developmental surveillance or milestone review of a child born before 37 weeks
Choosing the age at which to administer an age-banded screening questionnaire to a child born preterm
Plotting growth of a former preterm infant on term growth charts after the preterm-specific charts end

Formula

Weeks preterm = 40 − GA at birth (weeks) Corrected age = chronological age − weeks preterm Applies when GA < 37 weeks, until 24 months of chronological age (36 months if GA < 28 weeks) Months = days / 30.4375

Pearls & pitfalls

Correction uses 40 weeks as the reference: weeks preterm = 40 − gestational age at birth (AAP HealthyChildren.org).
A child born at 37 weeks or later is not corrected (preterm is defined as < 37 weeks in the Caderneta da Criança).
The correction period differs by gestational age in the Caderneta da Criança: up to 24 months of chronological age, or 36 months if born before 28 weeks.
Corrected age is never negative here: before term-equivalent age the result is shown as 0 and the postmenstrual age is the relevant measure.
When a screening instrument's manual gives its own rule for age adjustment, follow the manual for that instrument.

Next steps

Use the corrected age for milestones and age-banded screening while correction applies; after that period, use chronological age. When reporting, give both ages so that other clinicians can see which was used.

Evidence

The definition (chronological age minus the weeks born before 40 weeks) is given by the AAP (HealthyChildren.org, "Corrected Age For Preemies", adapted from Understanding the NICU, AAP 2017) and by the Caderneta da Criança 2025 (p. 79). The duration of correction (2 years; 3 years if gestational age < 28 weeks) is stated in the Caderneta da Criança 2025 (p. 90); the 2-year window is also given by the AAP page and by the DGS PNSIJ 2013 (Texto de apoio 1). These are consensus and programme documents, not trial evidence.

References

Brasil. Ministério da Saúde. Caderneta da Criança: Passaporte da Cidadania. 7ª edição revisada. Brasília: Ministério da Saúde; 2025 (pp. 78-79, 90). — link
American Academy of Pediatrics. Corrected Age For Preemies. HealthyChildren.org (last updated 12/10/2018). — link
Direção-Geral da Saúde. Programa Nacional de Saúde Infantil e Juvenil. Norma n.º 010/2013. Lisboa: DGS; 2013 (Texto de apoio 1). — link
Engle WA; AAP Committee on Fetus and Newborn. Age terminology during the perinatal period. Pediatrics. 2004;114(5):1362-1364. — link

Corrected Age for Preterm Infants

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