Premature Birth
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Premature Birth


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The normal gestation period for humans is about 40 weeks. Some babies are born before 40 weeks. Any birth that occurs more than three weeks before the due date, or before 37 weeks, is defined as a premature birth.

Amniotic Sac


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There are many reasons why a woman would go into labor before her scheduled due date, including:

  • Having previously delivered prematurely
  • A ruptured amniotic sac (ruptured membranes)
  • Infections of the urinary tract or cervix
  • A weak cervix—prior surgical procedures
  • Abnormalities in the uterus, including fibroids and malformations of the uterus
  • Twins or higher number of fetuses
  • Smoking, drinking, or using drugs during pregnancy—especially cocaine
  • Poor nutrition during pregnancy
  • Too much amniotic fluid (polyhydramnios)
  • Chronic diseases like:

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

The following factors increase your chance of delivering prematurely:

  • Having multiple births (twins, triplets, quadruplets, etc.)
  • Having a chronic disease
  • Having had a previous premature birth
  • Poor prenatal care, or poor nutrition during pregnancy
  • Substance abuse during pregnancy


Symptoms include:

  • Abdominal pain that feels something like menstrual cramps
  • Dull pain in the lower back
  • Pressure in the pelvis and tightening in the thighs
  • Vaginal bleeding or spotting, or watery discharge


Your doctor will ask about your symptoms and medical history, and perform a physical exam. Your obstetrician will to see if your cervix has dilated, and if fetal membranes have ruptured. Regularity of contractions will also be monitored, and an ultrasound may be performed.

Sometimes special tests are done, such as an ultrasound, to measure the cervix length, or fetal fibronectin (fFN).

The definition of preterm labor requires change in the dilation of the cervix under the influence of uterine contractions. Prior to actual preterm labor, the phrase threatened preterm labor may be used. Threatened preterm labor is potentially reversible.


Depending on how premature the delivery is, the doctor will talk to you about the risks associated with proceeding with the labor. If the fetus has developed enough to be able to live successfully outside of the uterus, the doctor will proceed with the labor. If it is too early and too risky to deliver, the doctor will try to stop the labor. Stopping labor is not simple. Often, the medications are not effective in preventing a preterm birth.

Sometimes when there is a risk of preterm deliver, the doctor will suggest giving a steroid medication to the mother. The medication can reach the fetus and cause maturation of the surfactant (a substance which prevents lung collapse) in the lungs.


To help reduce your chances of delivering your baby prematurely, take the following steps:

  • Get the proper prenatal care throughout your entire pregnancy
  • Eat a healthy, balanced diet with plenty of vitamins, minerals, and other nutrients
  • Avoid smoking, alcohol, and drugs
  • Keep chronic diseases under control
  • Reduce your stress level
  • Reduce activities as required by your doctor, such as cutting back on work or exercising less strenuously
  • Follow your doctor's recommendations about having sex during pregnancy


The American College of Obstetricians and Gyneclogists

The Nemours Foundation


British Columbia Ministry of Health

The Society of Obstetricians and Gynaecologists of Canada


Hall R. Prevention of premature birth: do pediatricians have a role? Pediatrics. 2000 May;105(5): 1137-1140. Available at: Accessed April 18, 2007.

Premature labor. American Pregnancy Association website. Available at: Accessed April 18, 2007.

Sheridan P. Rice sociologist finds premature birth increases risk for asthma. Rice University website. Available at: Accessed April 18, 2007.

Last reviewed April 2008 by Ganson Purcell Jr., MD, FACOG, FACPE

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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