What is preterm labor?

Preterm labor is labor that occurs before 37 weeks of pregnancy have passed. It is a concern because babies born prematurely are at higher risk of serious health complications.

If there are indications that preterm labor might occur, your doctor will use a range of medications to delay delivery for as long as possible, as every week that delivery can be delayed greatly reduces the risk of complications and increases the chances of survival for your baby.

This page focuses on the events leading up to a preterm birth. For more information about the birth process and what follows, see our premature birth and premature babies pages.

Causes

Causes of preterm labor include:

Infection

Entry into the body of microorganisms that can reproduce and cause disease.

Inflammation

A body’s protective immune response to injury or infection. The accumulation of fluid, cells and proteins at the site of an infection or physical injury, resulting in swelling, heat, redness, pain and loss of function.

Psychological

Relating to, arising in, or affecting the mind.

Stress

The word ‘stress’ can have a variety of meanings, but generally describes the physical and mental responses of the body to a demand placed upon it. Often used to describe conditions where the demand is high or unable to be resolved and creates anxiety and tension.

Uterus

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

Risk factors for preterm labor include:

Cervix

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

Fetal membranes

The membrane structures, including the amnion and chorion, which protect and nourish the developing fetus.

Uterus

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.

Cervical incompetence

Abnormal dilation of the cervix early in pregnancy, which can contribute to early birth.

Signs and symptoms

Signs and symptoms of preterm labor include:

  • Pelvic pressure;
  • Lower abdominal cramping and back pain;
  • Your waters breaking;
  • Changes in cervical discharge such that it is watery, bloody or mucus-like;
  • Dilation of the cervix;
  • Vaginal spotting, and;
  • Regular contractions of the uterus.

Preterm labour can cause lower abdominal cramping and vaginal spotting.Symptoms of preterm labor can include waters breaking and regular contractions. 

Cervix

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

Mucus

A thick, viscous liquid that is secreted for lubrication and to form a protective lining over certain tissues.

Uterus

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.

Pelvic

Relating to the pelvis, which is the bony structure in the lower part of the trunk. The pelvis connects the base of the spine to the legs, anchors the thigh and abdominal muscles and protects important organs such as the bladder and bowel (and in women, the uterus).

Abdominal

Relating to the abdomen, the middle portion of the trunk which contains organs such as the intestines, stomach and liver.

Methods for diagnosis

If contractions are frequent and intense enough to cause the dilation of the cervix between 24-37 weeks' pregnancy, it is a sign of preterm labor. A test called the vaginal fetal fibronectin test is performed on a swab of secretions near your cervix. The test detects fibronectin, which is a protein attached to the amniotic sac that surrounds your baby within the uterus. A positive result indicates an increased risk of preterm labor.

Sometimes a transvaginal ultrasound will also be performed to check your cervical length, since a short cervical length increases your risk of preterm labor.

The length of the cervix can indicate a risk of preterm labor. 

Amniotic sac

The bag that develops in the uterus during pregnancy, in which the fetus develops.

Cervix

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

Uterus

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.

Transvaginal ultrasound

An internal ultrasound of the female pelvis. An ultrasound probe is inserted into the vagina to get more detailed views of the inside of the pelvis.

Types of treatment

Labor can be delayed or stopped using medications known as tocolytic therapy. However, this is not used if labor is too advanced, or if your pregnancy is past 34 weeks. Tocolytic medications are intended to delay delivery for 48 hours. If by this time labor has stopped, you will be monitored until labor recommences.

Corticosteroids are given to reduce complications for your baby by helping the lungs mature faster. They are given between 24-34 weeks of pregnancy, often in conjunction with tocolytic medications.

Corticosteroids

A medication that resembles the cortisol hormone produced in the brain. It is used as an anti-inflammatory medication.

Potential complications

For the baby, potential complications of preterm labor include:

  • Immature lungs, which can result in breathing difficulties;
  • Pneumonia;
  • Anemia;
  • Infections;
  • Jaundice;
  • Bleeding in parts of the brain;
  • An immature digestive system that is unable to properly absorb nutrients, and;
  • Difficulty feeding, as the swallowing reflex has not yet developed. Premature babies may need to be fed through a tube inserted into their stomach.

Anemia

A deficiency in red blood cells or hemoglobin in the body.

Nutrients

Substances in foods that are necessary for the body to function and grow. They include macronutrients, which provide energy and micronutrients, which are substances needed in small amounts such as vitamins, minerals and trace elements.

Prognosis

If no complications occur, the prognosis is good for preterm birth beyond 34 weeks' pregnancy. The earlier you give birth, the greater the risk of complications. Even an extra week can make a big difference in reducing the risk of complications.

Prevention

You can reduce the risk of preterm labor by not smoking, not using recreational drugs and maintaining low stress levels. If you have a history of preterm labor, you might be given progesterone in the form of an injection or vaginal gel to help prevent it. This preventative treatment has not been proven to be effective for pregnant women who do not have a history of preterm labor.

Stress

The word ‘stress’ can have a variety of meanings, but generally describes the physical and mental responses of the body to a demand placed upon it. Often used to describe conditions where the demand is high or unable to be resolved and creates anxiety and tension.