What is premature birth?

Pregnancy normally lasts for a period of 37-42 weeks. After 37 weeks of pregnancy, it is called a 'term birth'. The premature birth of a baby is defined as occurring before 37 weeks. Depending on how early the premature birth occurs, the risk of complications for the child after birth is increased. Problems can occur due to the incomplete development of the baby's organs. This can involve breathing problems, difficulties staying warm or feeding, or injuries to the digestive system or nervous system. The exact cause of premature birth can often be difficult to identify, but causes can involve placental abruption, stretching of the uterus, infection in the uterus and sometimes stress.

This page focuses on the process of premature birth. For more information about the events leading up to a preterm birth see our preterm labor page. For more information about your preterm baby, see our premature babies page.

Nervous system

The extensive network of cells and structures that is responsible for activating and coordinating the body's functions, sensory input and cognition.


The hollow organ of the female reproductive system that is responsible for the development of the embryo and fetus during pregnancy. Also known as the womb.


The specific cause of premature birth can often be difficult to identify. Some causes can include:

  • Placental abruption, in which the placenta separates from the uterus;
  • Stretching of the uterus, which can occur from having twins or triplets in the uterus;
  • Infection of the uterus, which can produce substances that trigger premature birth, and;
  • Severe physical or psychological stress, which can trigger the release of hormones that bring on premature birth.


Relating to, arising in, or affecting the mind.


The hollow organ of the female reproductive system that is responsible for the development of the embryo and fetus during pregnancy. Also known as the womb.

Risk factors

The prediction of who will give birth to a premature baby is a difficult task. The largest risk factor is for women who have previously given birth to a premature baby. There is about a one in five chance that this will occur in another pregnancy. Other risk factors can include:

  • A twin or triplet pregnancy;
  • Previous surgery of the cervix;
  • Having excess amniotic fluid;
  • Cigarette smoking;
  • Using illicit drugs including cocaine;
  • A short interval since the last birth (12-18 months), and;
  • Being under 18 years old.

Amniotic fluid

The fluid surrounding and protecting the fetus inside the uterus during pregnancy.


The lower part of the uterus, leading out into the vagina.


Premature birth is sometimes classified as follows:

  • Moderate to late preterm, which is a pregnancy between 32-37 weeks' duration;
  • Very preterm, which is a pregnancy between 28-32 weeks' duration, and;
  • Extremely preterm, which is a pregnancy that is not longer than 28 weeks' duration.

Signs and symptoms

Premature birth means that the baby has not spent the regular amount of time inside the uterus. This means that the baby may not be fully developed or equipped for life after birth. Some signs that a baby's time in the uterus has been reduced include:

  • Small size with a head that is large in comparison;
  • Less rounded, sharper features;
  • Thin or transparent skin;
  • Difficulty breathing;
  • Jaundice;
  • Low body temperature after birth, and;
  • Reduced ability to suck and swallow.


The hollow organ of the female reproductive system that is responsible for the development of the embryo and fetus during pregnancy. Also known as the womb.

Methods for diagnosis

A diagnosis of premature birth can be made at birth by calculating the amount of time the baby has spent in the uterus. If a baby is born prematurely, certain tests may be carried out, including:

  • Monitoring breathing, heart rate and blood pressure;
  • Measuring the intake and output of fluid;
  • Blood tests, usually a heel prick to do a red blood cell count and check for anemia;
  • An ultrasound to view images of the baby's internal structures;
  • Echocardiography to view images of the baby's heart and check for any abnormalities, and;
  • An eye examination to check for any vision problems.


The procedure in which ultrasound waves are used to create an image of the heart, to allow assessment of the heart's function as it beats.


The hollow organ of the female reproductive system that is responsible for the development of the embryo and fetus during pregnancy. Also known as the womb.

Types of treatment

Depending on the initial health of a premature baby, specialized supportive care may be offered by a hospital and doctors in a neonatal intensive care unit (NICU). Some of the support and treatment can include:

  • Placing the baby in an incubator, also known as a humidicrib, which is an enclosed plastic bassinet. This will help to keep the baby warm and maintain a healthy body temperature;
  • Monitoring vital signs including breathing, heart rate and blood pressure;
  • Using a feeding tube for fluids and nutrients if the baby is unable to suck. This will also ensure that dehydration does not occur;
  • Blood transfusions to increase the number of red blood cells;
  • Medications, such as antibiotics if an infection occurs, and;
  • Surgery to correct specific issues, such as feeding, heart or vision problems.

Baby inside humidicrib incubator.Premature babies can be placed into a humidicrib to help maintain a healthy body temperature. 


The state of insufficient hydration; excessive loss of water; requiring more water in order to function normally.


The process of receiving blood or blood components from an external source directly into the bloodstream.

Potential complications

While not all premature babies experience complications, an early birth can result in an increased risk of developing some short- and long-term health conditions. Generally, the earlier a baby is born, the greater the risk of complications. Some complications may be evident at birth, while others may not be realized until later in life.

Short-term complications

The short-term complications related to premature birth can include:

  • Breathing problems, which can be due to an underdeveloped respiratory system;
  • Heart problems, including low blood pressure and patent ductus arteriosus, in which the hole between two major blood vessels that leave the heart fails to close after birth. This is more common for babies born before 30 weeks;
  • Brain problems, including bleeding in the brain and fluid accumulation. This is more common for babies born before 28 weeks;
  • Temperature control problems, particularly if your baby is born underweight. Underweight babies do not have as much stored body fat, which is used to keep warm;
  • Gastrointestinal problems, which are a result of an underdeveloped gastrointestinal system. This can result in injury of the cells that line the bowel when feeding. Feeding with breastmilk can reduce the risk of injury to the bowel, and;
  • Immature immune system, which can lead to infection. Infections can be treated with antibiotics.

Long-term complications

The long-term complications of premature birth can include:


The mental processes and abilities that are characterized by knowing and perceiving.


Relating to the stomach and intestines.


Relating to, arising in, or affecting the mind.


Although there is an increased risk of short- and long-term complications for babies who are born prematurely, not all babies experience these complications, or may only have a mild form of the complication. Healthcare today is very advanced and constantly evolving, so there are many effective monitoring and treatment tools available.


There is no specific way to prevent premature birth from occurring, but you can reduce the chance of it occurring by limiting risk factors in your control. This can include:

  • Obtaining prenatal care to identify any risks during your pregnancy;
  • Avoiding and quitting smoking, alcohol and illicit drugs;
  • Giving your body a rest between pregnancies by waiting at least 12-18 months between giving birth and becoming pregnant again;
  • Treating any infections as soon as they occur, and;
  • Avoiding stress where possible.

Currently, there are two tests that can help to predict a premature birth. These include using an ultrasound to measure the length of the cervix; the risk of premature birth decreases as the length of the cervix increases.

Another indicator involves measuring the level of fetal fibronectin, a protein that is produced by fetal cells, and appears in the vaginal discharge, prior to labor. Higher levels of fetal fibronectin indicate an increased risk of premature birth.


Before the birth of a baby.


The lower part of the uterus, leading out into the vagina.


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  4. Premature Birth Complications - Diseases and Conditions - Mayo Clinic. Accessed August 28 2014. http://www.mayoclinic.org/diseases-conditions/premature-birth/basics/complications/con-20020050.
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