Preterm Birth, Health, and Development


A baby born before the end of 37 weeks’ pregnancy is said to be born preterm, premature, or a “preemie”.

A preterm baby is born earlier than expected.

Some of the organs and body systems, like the brain and lungs, are therefore still immature. How immature depends on how early in the pregnancy he was born.

A baby’s brain grows tremendously in size and structure between the third trimester of pregnancy and 2 years of age. Nerve cells in the brain (called neurons) lengthen and sprout to form new connections, or synapses, with other neurons. They form an extensive network, a network that is more complex than that of any modern computer and that links all parts of the body and brain.

Here are a few ways of looking at age, considering the fact that some babies spend a lot less time growing in the womb than others.

Chronological age

The age you usually refer to on an ordinary basis, when celebrating birthdays and so on, is the time after birth, or the “chronological age”.

So, usually, if a baby is 8 weeks old, he was born 8 weeks ago.

In the case of a preemie, it becomes important to measure how long the baby was developing before birth as well as after. The terms “gestational age”, “postmenstrual age”, and “corrected age” are different ways of assessing milestones, health, and so on.

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What is gestational age?

Gestation is another word for pregnancy. “Gestational age” is the length of the pregnancy. It corresponds to the time the fetus spent in the womb, as calculated from the first day of the last menstrual period. Gestational age can be estimated from the ultrasound done in the first trimester of pregnancy and is used to confirm the expected due date.

At birth, the gestational age is calculated up to the date of delivery.
If a baby is born at 28 weeks of pregnancy, he is said to be 28 weeks’ gestational age.

What is postmenstrual age?

“Postmenstrual age” is “gestational age” + “chronological age”.

So, 8 weeks after birth, a baby born at 28 weeks’ gestational age is 28 + 8 = 36 weeks’ postmenstrual age.

What is corrected age?

“Corrected age”, or “adjusted age”, is the age the baby would have been if he had been born on the expected due date. It is used when comparing the milestones of a preemie to those of a child born full-term. In other words, you take into account the amount of time missing from his development in the womb.

“Corrected age” is “chronological age” minus the “amount missing”. The amount missing is also called a “correction factor”.  It is calculated by subtracting the number of weeks of gestation from 40, which is the number of weeks for a full-term pregnancy.

So, if a baby was born at 28 weeks of pregnancy, he was born 3 months early (40 – 28 = 12 weeks, or 3 months).
Ten months after birth, the corrected age is 7 months. This 10-month-old baby could be compared to a 37-month-old born full-term.

When is corrected age used?

Corrected age is used to check the preterm baby’s growth and development in the first two years after birth. As well, intestinal development and motor dexterity determine the foods a baby can digest, and both are still immature when a preemie is born. Introduction of the different food types is done using corrected age.

When is chronological age used?

Chronological age is used after the child’s second or third birthday, because as the years go by, the few months of age difference may not really matter. Chronological age is also used for scheduling vaccines, as immunity from maternal sources wears off sometime after birth.


Preterm babies, because they were born early, may or may not suffer from medical complications at and after birth, such as trouble breathing, infections, and so on, depending on how early they were born. Life in the outside world is very different from life in the mother’s womb.

Brain growth and maturation are affected by the child’s environment, experience, and general state of health. As the child grows and learns, nerve cells establish new connections.

Complications can be very stressful for both baby and parents. The combined stress of immaturity, complications requiring a stay in the NICU, and conditions inherent to life in the NICU itself, may affect body and brain development and impact later behaviours. This website offers preventive strategies that you can adapt for best results.

By far the greatest help you can give your baby at this time, and this applies to all preemies, is preventing infection. Repeated infections can cause setbacks.

Preventing infections

Your baby’s immune system is not yet fully developed and is still very weak.

Here are 10 easy steps to prevent infection in the NICU and at home. Be sure to follow them at all times:

  • Always wash your hands before taking care of the baby
  • Teach others to wash their hands properly before touching your baby
  • Avoid kisses on the baby’s hands and face
  • Tell people not to visit if they’re sick or have a cold
  • Tell people not to visit if they have diarrhea and/or vomiting
  • Tell people not to visit if they have a rash, a cold sore (herpes on the lip) or pink-eye (conjunctivitis)
  • Avoid crowded places, such as shopping malls, buses, and so on. Between November and April, especially, colds go around, including a bad cough known as bronchiolitis
  • Vaccinate your child
  • Get the flu vaccine for yourself and your family
  • If possible, don’t send your baby to daycare until his first birthday. In fact, if he had moderate-to-severe bronchopulmonary dysplasia (BPD) as an infant, try not to send him to daycare until age 2 years.

Babies born preterm or with health issues are at greater risk for developmental problems. These may or may not include motor (movement) delays or language, intellectual, social, or behavioural issues. Babies born extremely early are most at risk. Those born almost at term without complication present very little risk, if any.

Preventing developmental problems

Advances in medical science and technology have greatly improved prenatal care and available life-saving efforts for preterm infants and those with health issues.

Several approaches can foster development while the baby is in hospital and during early childhood. We suggest two guiding principles to follow:


  1. Developmentally-supportive care

Modify your child environment:

  • To reduce stress by avoiding excess light, noise, and pain.
  • To increase comfort levels by providing skin-to-skin contact (kangaroo care) or encouraging sucking, even when not feeding.
  1. Increase parent-infant bonding
  • Aim for activities that encourage bonding with your baby
  • Learn to recognize and interpret your baby’s behaviour
  • Find ways to best respond to your baby’s cues
  • Interact with your baby
  • Play. Enjoy life with baby and have fun!

Tip: Remember to use “corrected age” when looking at the various developmental stages.

The Best in Daily Life is intended to guide parents and families throughout the child’s first 2 years, based on best evidence and the guiding principles above.

  • Als H. Developmental care in the newborn intensive care unit. Curr Opin Pediatr. 1998;10: 138-42.
  • Rauh VA, et al. The Mother-Infant Transaction Program. The content and implications of an intervention for the mothers of low-birthweight infants. Clin Perinatol. 1990;17:31-45.
  • Spittle AJ, et al. Early developmental intervention programs post hospital discharge to prevent motor and cognitive impairments in preterm infants. Cochrane Database Syst Rev. 2007;2: CD005495.
  • Symington A, Pinelli J. Developmental care for promoting development and preventing morbidity in preterm infants. Cochrane Database Syst Rev. 2006;2: CD001814.

The following websites may be of interest.

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