How to Diagnose and Manage Preterm Labor

Posted On: August 9, 2023 By CIW

In this episode of the Healthful Woman podcast, maternal-fetal medicine specialists Dr. Nathan Fox and Dr. Jessica Spiegelman break down the definition of preterm labor and its treatment. Today, there are many medication options with pros and cons that can be considered for your individualized pregnancy care. Let’s discuss them in detail.

What is Preterm Labor?

According to Dr. Spiegelman, “anything under 37 weeks is considered preterm.” Preterm labor is defined as contractions that change the cervix during the time prior to 37 weeks. Many women have contractions at 37 weeks and earlier (especially those who have already had children) but if their cervix is not opening, this is not preterm labor.

Dr. Fox gives us a good example: “Let’s say you knew [the patient] was two centimeters dilated yesterday, and then they come in the next day contracting and they’re two centimeters dilated, I would not say they’re in preterm labor…because their cervix hasn’t changed.”

How is Preterm Labor Treated?

It is always a good idea to see your doctor if you are having painful contractions. They can perform a physical examination and monitor whether your cervix is continuing to dilate. About 50% of people in preterm labor will stop having contractions without any medical intervention. If contractions do not stop on their own and preterm labor is diagnosed, there are medications that can be given to optimize outcomes in case of a preterm delivery.


One of the most commonly recommended medications when someone is in preterm labor is steroids. Steroids do not actually treat preterm labor or contractions but reduce the risk of complications related to prematurity. Steroids help the fetal lungs mature and minimize the risk of other health problems associated with preterm birth. Doctors will determine whether someone is a candidate to receive steroids based on gestational age and whether the patient has previously received steroids. Typically, they will be administered as 2 injections, each given 24 hours apart (or 4 injections, each given 12 hours apart). They are at their most effective from 48 hours to 7 days after the first dose.

Magnesium Sulfate

Magnesium sulfate is a medication that can be given to reduce the risk of cerebral palsy in preterm infants. It’s important to recognize that, like steroids, magnesium will not stop labor. Though it does have an additional effect of decreasing contractions somewhat, that is not its primary purpose in this context. Often magnesium will be reserved for patients earlier than 32 weeks, but different institutions may have different protocols on who is eligible to receive magnesium. Magnesium is most effective if it is in the maternal circulation at the time of a preterm delivery. Magnesium can have some side effects (dizziness, flushing, nausea) so is usually stopped if imminent delivery is not suspected. (Magnesium sulfate is also used in the management of preeclampsia.)


Antibiotics are not used to prevent or stop preterm labor. However, they can be prescribed to prevent Group B Strep (GBS) infection in babies. Many adults are colonized with this bacterium; there is no way to know if someone is colonized with it without testing them for it. GBS is not harmful to adults but can lead to dangerous infections in newborns who are exposed to it, especially preterm infants. All pregnant patients are screened for GBS with a rectovaginal swab at around 36 weeks, but many people in preterm labor have not had this screening yet. If that is the case, or if someone is known to be GBS positive, antibiotics in labor can help reduce the risk of neonatal infection.


Medications known as tocolytics can also be used to try and slow down preterm labor. Tocolytics can counteract uterine contractions, but many of them have side effects and so cannot be used for long periods of time. Their primary purpose is to prevent preterm delivery for long enough for steroids to take effect (about 48 hours). They may not be universally effective but may increase the chances of the fetus receiving the full course of steroids prior to delivery. Some examples of tocolytics are nifedipine and indomethacin.


Nifedipine can relax the smooth muscle in the uterus to relieve painful contractions. Dr. Fox explains that as long as patients do not have negative side effects (like blood pressure that is too low, since nifedipine is a blood pressure medication as well), it can be a great solution to ease symptoms. Additionally, it may delay preterm delivery for long enough to give the full course of steroids.


Indomethacin is an NSAID. Long courses of NSAIDs are not recommended in pregnancy, but short courses can be safe. Indomethacin can be effective at easing contractions for that 48 hour window. Because of its potential impact on the fetal heart when given at the end of pregnancy, indomethacin is generally avoided after 30-32 weeks.

Schedule an Appointment

If you have any questions or concerns during your pregnancy, we encourage you to schedule an appointment with our team of OB-GYNs and maternal fetal health specialists. At Carnegie Imaging, we specialize in ultrasound and other forms of testing and can help you receive an accurate diagnosis.

Carnegie Imaging for Women blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!

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