Tocolytics are drugs that are used to delay your delivery for a short time (up to 48 hours) if you begin labor too early in your pregnancy.
Doctors use these drugs to delay your delivery while you are being transferred to a hospital that specializes in preterm care, or so that they can give you corticosteroids or magnesium sulfate. The corticosteroid injections help mature the baby’s lungs.
Magnesium sulfate protects a baby under 32 weeks from cerebral palsy, but it can also be used as a tocolytic. Magnesium sulfate is also used to prevent seizures in pregnant women with preeclampsia (high blood pressure).
Other drugs that can be used as a tocolytic include:
- beta-mimetics (for example, terbutaline)
- calcium channel blockers (for example, nifedipine)
- non-steroidal anti-inflammatory drugs or NSAIDs (for example, indomethacin)
General information about these drugs is given below.
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 given especially if a woman is at low risk of delivering her baby early. For women at high risk of delivering within the next week, magnesium sulfate (administered intravenously) is usually the drug of choice.
Tocolytic medications for preterm labor aren’t used before 24 weeks of pregnancy. In certain situations, your doctor may use it when you are at 23 weeks of pregnancy.
Many doctors stop giving tocolytics after a woman has reached her 34th week of pregnancy, but some doctors begin tocolytics as late as 36 weeks.
Your doctor may first try treating your preterm labor with bed rest, extra fluids, pain medicine, and a single dose of a tocolytic medication. They 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 corticosteroid medication to improve the baby’s lung function.
If the contractions stop, your doctor will reduce and then 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.
No tocolytic medication has been shown to consistently delay delivery for a significant period of time.
However, tocolytic medications can delay delivery for at least a short while (usually a few days). This usually provides enough time to receive a course of steroids. The corticosteroid injections reduce the risks for your baby if they arrive early.
Women should not use tocolytic medications when the risks of using the medications outweigh the benefits.
These complications may include women with severe preeclampsia or eclampsia (high blood pressure that develops during pregnancy and can cause complications), severe bleeding (hemorrhage), or infection in the womb (chorioamnionitis).
Tocolytic medications should also 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 centimeters or more
The doctor may still use tocolytics when the baby has an abnormal heart rate (as shown on the fetal monitor), or slow growth.