Premature babies

What does it mean to be a premature baby?

Babies are usually born around 40 weeks after conception; this is called full-term. Premature babies are born early. They face extra challenges as they adapt to the outside world before they are ready. Compared with full-term babies, they have underdeveloped muscles, less fat, reduced stamina, and more sensitivity to stress. Babies born at 38 weeks or less often cannot breastfeed well enough to get the milk they need to grow well. They may need extensive, specialized help and often spend time in a hospital’s neonatal intensive care unit. They are also at higher risk of illnesses such as blood infections and gut disease and may face longer-term challenges such as delayed development and lung damage. They benefit greatly from breast milk and breastfeeding.

A) Describing the premature baby

Babies are usually born about 40 weeks after conception (term babies). Premature babies are born early. They are also known as:

  • Premies
  • Preemies
  • Preterm babies

The number of babies born before 38 weeks ranges from 5% to 18% of all babies born across 184 countries (WHO/UNICEF 2017).

1) Possible reasons for an early birth

The exact reason for having a premature birth is unknown but some risk factors have been identified:

  • Being younger than 18 or older than 35
  • Having a previous premature baby
  • Being pregnant with more than one baby
  • An interval of less than six months between pregnancies
  • Certain structural abnormalities of the uterus, cervix, or placenta
  • Some infections including sexually transmitted diseases
  • In vitro fertilization
  • High blood pressure
  • Diabetes
  • Being under- or overweight
  • Smoking and substance use disorder
  • Physical injury
  • Air and environmental pollution (Liu 2019; Padula 2018)

2) Describing babies by age after conception

It is important for health-care providers and health systems to be able to classify the age of a baby at birth (the number of weeks since conception). The terms in the following table are generally accepted for describing a baby’s age at birth (ACOG 2015; WHO 2017).

Table: Categories Describing Babies’ Age at Birth

Even though babies between 37 and 38 6/7 weeks are called early term, these babies are at high risk of breastfeeding problems.

3) Describing babies by weight

Health-care providers also consider weight when assessing a newborn baby. Babies who weigh less than 2,500 grams (5 pounds 8 ounces) are considered as having a low birth weight. Causes of low birth weight include:

  • Premature birth
  • Slow growth caused by:
    • The placenta not providing enough nutrients
    • Illness in the baby
    • Illness in the mother
    • Air pollution (Hao 2019; Rich 2009)

Babies who have slow growth weigh less than expected for their gestational age. They are often called small for gestational age (SGA). The following table lists the categories used to describe the birth weight of babies.

Table: Categories Describing Babies’ Weight at Birth

B) Consequences of being born early

1) Immature brain and nervous system

Premature babies face extra challenges as they adapt to the outside world before they are fully ready. Compared with full-term babies, they are neurologically immature. At 34 weeks, the brain is only about two-thirds of the weight of a full-term baby’s brain. Between 30 and 40 weeks, the amount of myelin increases by five times (Adams-Chapman 2006). Myelin is a fatty white substance that is critical for nerve conduction and brain function.

2) Other challenges caused by being born early

Compared with full-term babies, premature babies also have:

  • Underdeveloped muscles
  • Less fat
  • Thinner skin
  • Reduced stamina
  • Poor co-ordination of sucking, swallowing, and breathing
  • More sensitivity to bright lights, loud noises, and other types of stress (Morag 2016)
  • More difficulty latching, staying latched, and getting milk from the breast
  • Less able to show signs of pain (Jones 2017)
  • A gut that is particularly at risk of injury and inflammation

3) Consequences of being born immature

As a result of these challenges, babies born at 38 weeks and less are often unable to breastfeed well enough to get the amount of milk they need to grow well. They are less likely to be breastfed and are more likely to breastfeed for shorter periods (Fan 2019).

They may need help with breathing, keeping warm, preventing and treating infections, and other complications of an early birth.

Premature babies are often cared for in a hospital’s neonatal intensive care unit (NICU). Doctors, nurses, and other health-care providers who work in hospitals have specialized training in caring for vulnerable babies and have an important role in ensuring the best outcomes (Weber 2018).

The nature of the hospital can impact breastfeeding. Mothers are more likely to breastfeed exclusively when provided with single-family rooms while in hospital (van Veenendaal 2019). Breastfeeding support can also be variable. 

C) Illness in premature babies

Premature babies are at a higher risk of short- and long-term health challenges. Breastfeeding and breast milk feeding can prevent or reduce many of these.  

1) Immediate health challenges

Short-term challenges may include:

2) Longer-term health challenges

Longer-term challenges may include:

  • Delayed physical development
  • Impaired brain and neural development (Spittle 2015)
  • Cerebral palsy
  • Vision (retinopathy of prematurity) and hearing problems
  • Asthma
  • Lung damage (bronchopulmonary dysplasia)
  • Intestinal damage
  • Feeding problems

3) Long-term challenges

Being born prematurely exposes the baby to many stressors. These may result in permanent changes in their body structure and function and an increased risk of adult chronic diseases. Adults who were born prematurely are more likely to develop (Luu 2017):

  • Heart disease
  • Kidney disease
  • Diabetes
  • Mental health challenges

D) Considerations for breastfeeding premature babies

Premature babies face many challenges and benefit greatly from breastfeeding and receiving breast milk.

In 2012, the Baby-Friendly Hospital Initiative for Neonatal Wards was established and made recommendations to improve  breastfeeding support  for preterm and ill babies, but not all hospitals follow these recommendations (Maastrup 2018).

Considerations for breastfeeding premature babies and supporting their families include:


Adams-Chapman I. Neurodevelopmental outcome of the late preterm infant. Clin Perinatol. 2006 Dec;33(4):947-64; abstract xi
American College of Obstetricians and Gynecologists (ACOG). ACOG Committee Opinion No 579: Definition of term pregnancy. Obstet Gynecol 2013; 122:1139–40. Reaffirmed 2015
Fan HSL, Wong JYH, Fong DYT, et al. Association between early-term birth and breastfeeding initiation, duration, and exclusivity: A systematic review. Birth. 2019 Mar;46(1):24-34
Hao J, Zhang F, Chen D, et al. Association between ambient air pollution exposure and infants small for gestational age in Huangshi, China: a cross-sectional study. Environ Sci Pollut Res Int. 2019 Nov;26(31):32029-32039
Jones L, Fabrizi L, Laudiano-Dray M, et al. Nociceptive Cortical Activity Is Dissociated from Nociceptive Behavior in Newborn Human Infants under Stress. Curr Biol. 2017 Dec 18;27(24):3846-3851.e3
Liu Y, Xu J, Chen D, et al. The association between air pollution and preterm birth and low birth weight in Guangdong, China. BMC Public Health. 2019 Jan 3;19(1):3
Luu TM, Rehman Mian MO, Nuyt AM. Long-Term Impact of Preterm Birth: Neurodevelopmental and Physical Health Outcomes. Clin Perinatol. 2017 Jun;44(2):305-314
Maastrup R, Haiek LN, Lubbe W, et al. Compliance with the Baby-friendly Hospital Initiative for Neonatal Wards (Neo-BFHI): A cross-sectional study in 36 countries. Matern Child Nutr. 2018 Sep 10:e12690
Morag I, Ohlsson A. Cycled light in the intensive care unit for preterm and low birth weight infants. Cochrane Database Syst Rev. 2016 Aug 10;(8):CD006982
Padula AM, Huang H, Baer RJ, et al. Environmental pollution and social factors as contributors to preterm birth in Fresno County. Environ Health. 2018 Aug 29;17(1):70
Rich DQ, Demissie K, Lu SE,et al. Ambient air pollutant concentrations during pregnancy and the risk of fetal growth restriction. Journal of epidemiology and community health. 2009;63:488–496
Spittle A, Orton J, Anderson PJ, et al. Early developmental intervention programmes provided post hospital discharge to prevent motor and cognitive impairment in preterm infants. Cochrane Database Syst Rev. 2015 Nov 24;(11):CD005495
van Veenendaal NR, Heideman WH, Limpens J, et al. Hospitalising preterm infants in single family rooms versus open bay units: a systematic review and meta-analysis. Lancet Child Adolesc Health. 2019 Mar;3(3):147-157
Weber A, Harrison TM, Sinnott L, et al. Associations Between Nurse-Guided Variables and Plasma Oxytocin Trajectories in Premature Infants During Initial Hospitalization. Adv Neonatal Care. 2018 Feb;18(1):E12-E23
WHO/UNICEF. Preterm birth; Fact Sheet. Geneva: World Health Organization; 2017