Treatment of Preterm Labor: Tocolytics

Tocolytic Medication

Tocolytic medications are drugs that slow contractions. They come in several different classes:

  • beta-mimetics (for example, terbutaline);
  • magnesium sulfate;
  • calcium channel blockers (for example, nifedipine); and
  • non-steroidal anti-inflammatory drugs or NSAIDs (for example, indomethacin).

General information about these drugs is given below.

What Kind Of Tocolytic Medication Should Be Used?

There is no data showing that one drug is consistently better than another, and doctors in different parts of the country have different preferences. In many hospitals, terbutaline is the drug given first, especially if a woman is at low risk of delivering her baby early. For women at high risk, magnesium sulfate (administered intravenously) is usually the drug of choice.

At What Point During My Pregnancy Can I Take Tocolytic Medications?

Tocolytic medications for preterm labor should not be used before 17 to 20 weeks of pregnancy (guidelines vary between institutions). Many doctors avoid giving tocolytics after a woman has reached her 34th week of pregnancy, but some doctors begin tocolytics as late as 36 weeks.

How Long Should Tocolytic Medications be Continued?

Your doctor may first try treating your preterm labor with bedrest, extra fluids, pain medicine, and a single dose of a tocolytic medication. He or she may also do further screening (like a fetal fibronectin test and transvaginal ultrasound) to better determine your risk for preterm delivery. If your contractions do not stop, the decision to continue tocolytic medicines and for how long will be based on your actual risk of preterm delivery (as determined by the screening tests), the age of the baby, and the status of the baby's lungs.

If tests indicate that you are at high risk for preterm delivery, your doctor will probably give you magnesium sulfate for at least 24 to 48 hours as well as steroid medication to improve the baby's lung function. If the contractions stop, your doctor will probably discontinue magnesium sulfate. If contractions continue, your doctor may order additional tests to rule out underlying infection in the uterus. The doctor may also do a test to determine the status of the baby's lungs.

How Successful Are Tocolytic Medicines?

No tocolytic medication has been shown to consistently delay delivery for a significant period of time. However, the drugs described on this map can delay delivery for at least a short while (usually a few days). This usually provides enough time to receive a course of steroids. Steroids injections reduce the risks for your baby if he or she arrives early. For more information on the effects of steroids on the baby, go to Corticosteroids.

Who Should Not Use Tocolytic Medications?

Women should not use tocolytic medications when the risks of using the medications outweigh the benefits. This would include women with severe preeclampsia or eclampsia (high blood pressure that develops during pregnancy and damages the mother), severe bleeding (hemorrhage), or infection in the womb (chorioamnionitis). Also, tocolytic medications should not be used if the baby has died in the womb or if the baby has an abnormality that will lead to death after delivery.

In other situations, a doctor may be cautious about using tocolytic medications, but may prescribe them because the benefits outweigh the risks. These situations may include when the mother has:

  • mild preeclampsia
  • relatively stable bleeding during the second or third trimester
  • serious medical conditions
  • a cervix that has already dilated 4 to 6 cms or more

Or when the baby has:

  • an abnormal heart rate (as shown on the fetal monitor) or
  • slow growth

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