Women's Healthcare Topics

Preterm Labor Risks, Causes, Predicting and Treatments

Reviewed by James Brann, M.D.

What should I know about preterm labor?

Preterm labor is defined as contractions that begin before 37 weeks of pregnancy and a term pregnancy is defined between 37 to 42 weeks. Your due date is calculated as the 40th week of pregnancy.

Most babies are delivered around their due date, but 12 percent of pregnancies are delivered before 37 weeks, which is considered preterm.  Most preterm labor women do not actually go on to deliver their babies early. It is estimated that only 30 to 50 percent of women in preterm labor cannot be stopped and go on to give birth.

A preterm baby is at risk for problems that include a difficult time breathing, difficulty maintain a normal body temperature, feeding problems, as well as more serious problems to the eyes, intestines and central nervous system.

Peterm Labor Risk Factors

It is not known exactly why preterm labor starts, but we do know some of the risk factors associated with preterm labor. One of the biggest risk factor is having delivered a previous preterm baby. It is known that 22 percent of women with a previous preterm delivery will go on to have another preterm delivery.

Risk factors of preterm delivery include:

  • If you are carrying multiples

  • A previous cervical conization for abnormal pap smears

  • Uterine abnormalities, such as fibroids, polyps or septum

  • Bleeding late in your pregnancy

  • Illicit drugs usage in pregnancy, such as cocaine

  • Abuse of tobacco, smoking cigarettes

  • Various infections

  • Being underweight before pregnancy, and poor weight gain during pregnancy

  • Excessive amount of amniotic fluid

  • Anemia in the first part of pregnancy

  • Less than 12 months from you last pregnancy

  • Young women between 18 to 20 years old

What Causes Preterm Labor?

The exact cause of preterm labor in most situations is difficult to identify. But there are four characteristics that may trigger preterm labor.

  • Bleeding — from either a placenta previa (when the afterbirth is near the cervix or opening of the uterus) or placental abruption (the separation of the afterbirth from the wall of the uterus) the amniotic sac (the sac the baby is in) can rupture and cause preterm labor.

  • Stretching of the uterus greater than normal – If you have twins, or multiples, or have an excessive amount of amniotic fluid your uterus will stretch more than normal. It is believed that this stretching releases substances that lead to preterm contractions and labor.

  • Bacterial infection—of the uterus or amniotic sac can produce chemical triggers that start preterm labor contractions.

  • Both Physical and/or psychological stress — can trigger the release of hormones that cause contractions and preterm labor.

Predicting Preterm Labor

Learn about the risks for preterm labor.

Two tests are available to help predict if you will have preterm labor, Fetal Fibronectin testing and measuring the cervical length.

  • Fetal Fibronectin - Prior to labor a chemical called fetal fibronectin is released. If this substance is not found in vaginal fluid then preterm birth is unlikely. If it is found, there is an increase chance of early delivery, but not always.

  • Cervical length – By using an ultrasound you can measure the cervical length If it is found to be shorter than normal there is a risk of preterm labor.

What are the Signs of Preterm Labor?

  • Increase in watery or bloody vaginal discharge

  • Increasing lower abdominal pressure

  • Persistent low backache

  • Menstrual like cramping associated with or without diarrhea

  • Contractions that have become regular and frequent

  • Bag of water breaks (ruptured membranes) feels like a gush of water

How is Preterm Labor Treated?

Your physician will either try to stop or slow down your preterm labor by giving you medicines called “tocolytic agents.”

Also, if you are between 23 and 34 weeks pregnant, your physician will administer steroid medications to help with the development of your baby’s lungs.

Tocolytic Medicines for Stopping Preterm Labor

When you are in preterm labor you will be admitted to the hospital and tocolytic medications will be administered to stop your labor.  The most common tocolytic medicines include terbutaline, magnesium sulfate,nifedipine, and indomethacin. You will need to have placed an intravenous line to give these medicines and extra fluids. The baby’s heart beat will be monitored as well as your contractions.

If your labor is stopped you will be monitored in the hospital afterward to make sure your contractions do not restart. When you are finally discharged from the hospital you will be asked to limit your activities and report any contractions to your healthcare provider.

You can monitor yourself  at home for contractions by lying down and placing your fingertips on your uterus. The uterus should be soft and relaxed. If you are not having contractions you will be able to easily indent your uterus with your fingertips. With a contraction the uterus forms a hard ball and is difficult to push in.

Steroids for Fetal Lung Maturity

The maturation of your baby’s lungs with steroids will help your baby breathe if born early. The most widely given steroid is betamethasone. An interesting note, the steroids used to develop a baby’s lung are not the same as the steroids athletes use.

Steroids are given by a shot and most be administered several hours before your baby is born.  You will receive two doses that are giving 24 hours apart. The best benefit is seen when the shots are given 48 hours before your baby is born.

Preterm Labor Prevention

It is hard to prevent preterm labor, but one of the most beneficial things you can do is to stop habits that could be harmful, like the use of illegal drugs and smoking.

If you have a history of previous preterm labor your physician can give you a progesterone supplement to prevent another early delivery. The progesterone supplement can be given as an injection or a vaginal gel that is administered starting between your 16th to 26th weeks of pregnancy. The progesterone supplement is continued until you reach 36 weeks.


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