What Does Gestational Age Really Mean in the NICU?
In the NICU, “gestational age” is one of those phrases you hear early and then hear constantly. Parents are asked about it and care plans are made for babies based on it - so understanding it can make a lot of NICU conversations feel less confusing.
What gestational age means
Gestational age refers to how far along a pregnancy was at the time a baby was born. It’s measured in weeks, starting from the first day of the mother’s last menstrual period.
In the NICU, gestational age is used as a way to understand a baby’s developmental maturity — not their size, strength, or how they’re doing on any given day.
Why gestational age matters in the NICU
Many body systems develop on a general timeline, and gestational age helps the care team anticipate what a baby may still be working on.
It’s commonly used to help think about:
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Lung development and breathing support
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Feeding readiness and coordination
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Patterns of apnea and bradycardia
Babies born around 37–40 weeks of pregnancy are considered full term. Babies born before that are considered premature, meaning they arrived before development was complete. Some babies are born much earlier in pregnancy — often called extremely premature — when organs like the lungs, brain, and nervous system are still very immature. Because development changes so quickly week to week, gestational age gives the NICU team important context for what a baby may still be growing into.
Gestational age doesn’t determine outcomes on its own. It provides context for what’s typical at different stages of development.
How gestational age is used in day-to-day care
Gestational age shapes a lot of everyday NICU conversations.
NICU staff track gestational age closely because many changes in breathing, feeding, stamina, and regulation tend to follow developmental timing more closely than calendar time since birth.
You’ll often hear gestational age referenced when talking about:
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When feeding skills may start to emerge
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How breathing support might change over time
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Growth expectations
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Discharge readiness
It’s one of several reference points the team uses — not a scorecard and not a prediction.
What gestational age does not tell you
Gestational age alone can’t tell you:
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Exactly how long your baby will stay in the NICU
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When specific milestones will happen
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What long-term outcomes will be
Those answers depend on how an individual baby progresses, not just a number on a chart.
A quick orientation to the different “ages” you’ll hear
In the NICU, babies are often described using more than one kind of age.
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Gestational age helps the team understand developmental maturity. Staff track this number every day your baby is in the NICU.
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Chronological age counts the days and weeks since birth. You’ll likely hear this as the number of days since birth (Day of life 7, or day of life 22, etc)
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Corrected age is a way of adjusting expectations for babies born early. A baby might be two months old on the calendar, but still not past their due date, which can make things feel confusing. You can read more about corrected age here.
Each one matters, but they’re used for different reasons. This article focuses on gestational age, because it’s the number NICU staff reference constantly when thinking about development.
Bottom line
Gestational age is a shared language NICU teams use to talk about development. It helps set expectations and guide care, but it doesn’t define your baby or their future.