What is preterm labor?
Preterm labor is labor that comes too early—between 20 and 37 weeks of pregnancy. In labor, the uterus contracts to open the cervix. This is the first stage of childbirth. In most pregnancies, this happens at 37 to 42 weeks. Preterm labor is also called premature labor.
Preterm labor doesn't always lead to preterm birth, but it may. A baby born too early may have serious problems, such as chronic lung disease. This is because many of the baby's organs, especially the heart and lungs, aren't fully grown yet. The earlier a baby is born, the higher the risk of problems.
What causes it?
Preterm labor can be caused by a problem involving the baby, the mother, or both. Possible causes of preterm labor include being pregnant with more than one baby, an infection, and problems with the placenta, uterus, or cervix. Often a combination of several factors is responsible. Sometimes the cause isn't known.
What are the symptoms?
It can be hard to tell when labor starts. But you may notice one or more symptoms, such as menstrual-like cramps, leaking or gushing of fluid from your vagina, or regular contractions. This means about 6 or more contractions in 1 hour, even after you've had a glass of water and are resting.
How is it diagnosed?
If you have symptoms of preterm labor, both you and your baby will be examined and monitored. You may have urine and blood tests to check for problems that can cause preterm labor. Your doctor or midwife will check the baby's heartbeat and do an ultrasound to see how your baby is doing.
How is preterm labor treated?
Preterm labor isn't always treated. When deciding whether and how to treat it, many things are considered, including your health and your baby's age, weight, and health. Your doctor or midwife may use medicine to try to delay the birth or medicines to prevent infection and prepare your baby for birth.
Preterm labor can be caused by a problem involving the baby, the mother, or both. Often a combination of several factors is responsible. Sometimes the cause isn't known.
Possible causes of preterm labor include:
- The placenta separating early from the uterus. This is called placenta abruptio.
- Being pregnant with more than one baby, such as twins or triplets.
- An infection in the mother's uterus that leads to the start of labor.
- Problems with the uterus or cervix.
- Drug or alcohol use during pregnancy.
- The mother's water (amniotic fluid) breaking before contractions start.
It's hard to prevent preterm labor, because it usually isn't expected. Also, it's often due to causes that aren't completely understood.
But building some healthy pregnancy habits—such as going to all of your doctor appointments—may help prevent preterm labor and give your baby the best chance to be healthy.
Being pregnant with twins, triplets, or more increases the chances of preterm labor and problems for the babies.
If you had preterm labor in a previous pregnancy, your risk for having it again is high. Your doctor may consider giving you progesterone during your second and third trimesters. This may help lower your risk of preterm labor.
But if you're pregnant with twins or more, progesterone treatment is generally not used to prevent preterm labor even if you had a previous preterm birth. Progesterone does not prevent preterm birth in women pregnant with more than one baby.
It can be hard to tell when labor starts, especially when it starts early. But you may notice one or more symptoms, including:
- Regular contractions. This means about 6 or more in 1 hour, even after you've had a glass of water and are resting.
- Leaking or gushing of fluid from your vagina. It may be pink or reddish.
- Menstrual-like cramps, with or without diarrhea.
- A feeling of pressure in your lower belly.
- A persistent, dull ache in your lower back, pelvic area, lower belly, or thighs.
- Changes in your vaginal discharge. It may increase in amount or become pink or reddish.
If your contractions stop, they may have been Braxton Hicks contractions. They're like practice contractions. But sometimes it can be hard to tell the difference.
If preterm labor occurs close to your due date (in the 35th or 36th week of pregnancy), you may be allowed to deliver without delay. Preterm birth at this point in a pregnancy doesn't usually cause serious problems.
But preterm labor doesn't always mean that preterm birth will happen. Your doctor may be able to stop your preterm labor.
When preterm labor can't be stopped, most women can deliver vaginally. But if your health or your baby's health is at risk, you may need a cesarean section.
If a baby is born too early, the baby may have complications, such as bleeding in the brain or chronic lung disease. The earlier a baby is born, the higher the risk.
When to Call a Doctor
Preterm labor can be hard to recognize. Get the earliest possible medical care by calling your doctor or your nurse-midwife about signs of preterm labor.
Anytime during your pregnancy
Call your doctor or your nurse-midwife if:
- Your water breaks.
- You have bleeding or spotting from your vagina.
- You have painful or frequent urination or your urine is cloudy, foul-smelling, or bloody.
Between 20 and 37 weeks of your pregnancy
Call your doctor, your nurse-midwife, or the labor and delivery unit of your local hospital if:
- You have had regular contractions for an hour. This means about 6 or more in 1 hour, even after you have had a glass of water and are resting.
- You have unexplained low back pain or pelvic pressure.
- You have symptoms of infection. For example:
- Your belly hurts when you press on it.
- You have a fever that you can't explain.
- You feel unusually tired.
- You have intestinal cramps.
- The baby has stopped moving or is moving much less than normal. Your doctor can tell you about kick counting, which you can use to check your baby's activity.
If you are having painless or mild contractions that are irregular or more than 15 minutes apart:
- Stop what you are doing.
- Empty your bladder.
- Drink 2 or 3 glasses of water or juice. (Having too little body fluid can cause contractions.)
- Lie down on your left side for at least an hour, and keep track of how often you have contractions.
If your contractions stop, they were probably Braxton Hicks contractions. These are harmless and normal. Braxton Hicks contractions are often irregularly timed and uncomfortable rather than painful.
Call your doctor or nurse-midwife if you start to have regular contractions.
Exams and Tests
If you think you have symptoms of preterm labor, your doctor or certified nurse-midwife can check to see if your water has broken, if you have an infection, or if your cervix is starting to dilate. You may also have urine and blood tests to check for problems that can cause preterm labor.
Your doctor or midwife will check the baby's heartbeat and do an ultrasound to see how your baby is doing.
You may have a painless swab test for a protein in the vagina called fetal fibronectin. If the test doesn't find the protein, then you are unlikely to deliver soon. But the test can't tell for certain if you are about to have a preterm birth.
Preterm labor isn't always treated. When deciding whether and how to treat it, many things are considered, including your health and your baby's age, weight, and health.
If you are in preterm labor, your doctor or certified nurse-midwife must compare the risks of early delivery with the risks of waiting to deliver. Depending on your situation, your doctor or midwife may:
- Try to delay the birth with medicine. This may or may not work.
- Use antibiotics to treat or prevent infection. If your amniotic sac has broken early, you have a high risk of infection and must be watched closely.
- Give you steroid medicine to help prepare your baby's lungs for birth.
- Treat any other medical problems that are causing trouble in the pregnancy.
- Let the labor go on if delivery is safer for you and your baby than letting the pregnancy go on.
When you first have symptoms of preterm labor
Symptoms of preterm labor are warning signs. They don't necessarily mean that you'll have a preterm birth.
If you're less than 37 weeks pregnant and you're having more or stronger contractions than usual, try these things.
- Drink 2 or 3 glasses of water.
Not having enough liquids can cause contractions.
- Lie down and rest on your left side for at least 1 hour.
If your contractions get worse during the hour, call your doctor or nurse-midwife, or go to the hospital.
- Do what you can to reduce stress.
Although stress isn't thought to be a direct cause of preterm labor, try to do less, ask for help, and eat well.
If your contractions are causing changes in your cervix, or if you have signs of infection or preterm prelabor rupture of membranes (pPROM), you may be given medicines to help delay delivery.
Delaying labor even for a short time can allow you to be:
- Moved to a medical center that has a neonatal intensive care unit (NICU).
- Given medicine to speed up lung development, which takes at least 48 hours to fully benefit the baby's lungs. Even 24 hours provides some benefit.
Medicines that may be used to treat preterm labor include:
- Antibiotics to prevent or treat infection.
- Antenatal corticosteroids, to help prepare the fetus's lungs for preterm birth.
Tocolytic medicines, to stop preterm labor. Examples include:
- Magnesium sulfate. If you're less than 32 weeks pregnant, your doctor or nurse-midwife may give you this medicine to help prevent some problems that affect your baby's brain, such as cerebral palsy.
Certain tocolytic medicines can be dangerous when a fetus is showing signs of distress or for women with certain health conditions (such as heart problems, severe preeclampsia, or poorly controlled diabetes or high blood pressure).
Current as of: February 23, 2022
Author: Healthwise Staff
Sarah Marshall MD - Family Medicine
Kathleen Romito MD - Family Medicine
Adam Husney MD - Family Medicine
Elizabeth T. Russo MD - Internal Medicine
Kirtly Jones MD - Obstetrics and Gynecology