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This topic covers how preterm labor affects the pregnant woman. If you want to know how it affects the baby after he or she is born, see the topic Premature Infant.
What is preterm labor?
Preterm labor is labor that comes too early—between 20 and 37 weeks of pregnancy.
Preterm labor is also called premature labor.
What are the risks of preterm labor and preterm birth?
The earlier a baby is delivered, the higher the chances are that he or she will have serious problems. This is because many of the baby's organs—especially the heart and lungs—aren't fully grown yet.
For infants born before 24 weeks of pregnancy, the chances of survival are extremely slim. Many who do survive have long-term health problems. They may also have trouble with learning and talking and with moving their body (poor motor skills).
What causes preterm labor?
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.
Often the cause isn't known.
Sometimes a doctor uses medicine or other methods to start labor early because of pregnancy problems that are dangerous to the mother or her baby.
What are the symptoms?
It can be hard to tell when labor starts, especially when it starts early. So watch for these symptoms:
- 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.
- Leaking or gushing of fluid from your vagina. You may notice that it is pink or reddish. This is called a rupture of membranes, also known as your water breaking. When this happens before contractions start, it's called premature rupture of membranes, or PROM. When it happens before 37 weeks of pregnancy, it is called preterm premature rupture of membranes, or pPROM.
- Pain that feels like menstrual cramps, with or without diarrhea.
- A feeling of pressure in your pelvis or lower belly.
- A dull ache in your lower back, pelvic area, lower belly, or thighs that doesn't go away.
- Not feeling well, including having a fever you can't explain and being overly tired. Your belly may hurt when you press on it.
If your contractions stop, they may have been Braxton Hicks contractions. These are a sometimes uncomfortable—but not painful—tightening of the uterus. They are like practice contractions. But sometimes it can be hard to tell the difference.
How is preterm labor diagnosed?
If you think you have symptoms of preterm labor, call your doctor or certified nurse-midwife. He or she 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.
Checking the baby's heartbeat and doing an ultrasound can give your doctor or midwife a good picture of 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.
How is it treated?
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 causing trouble in pregnancy.
- Allow the labor to go on because delivery is safer for the mother and baby than letting the pregnancy go on.
Preterm labor can be caused by a problem involving the baby, the mother, or both. Often a combination of several factors is responsible. But in about 1 out of 3 preterm births, the cause isn't known.footnote 1
Causes of preterm labor include:
- Being pregnant with more than one baby. Women who are pregnant with more than one baby have an increased risk of complications—both for the mother and the babies—and typically deliver early.
- Infection, which can trigger uterine contractions and preterm premature rupture of membranes (pPROM). This may include:
- Placenta abruptio. This is the early separation of the placenta from the uterus.
- The use of drugs such as cocaine or methamphetamine.
- Problems with the uterus or cervix, such as:
Preterm labor often starts without obvious symptoms. But you may notice one or more symptoms, including:
- Menstrual-like cramps, with or without diarrhea.
- A feeling of pressure in your pelvis or lower belly.
- A persistent, dull ache in your lower back, pelvic area, lower belly, or thighs.
- Changes in your vaginal discharge, which may increase in amount or become pink or reddish.
- Regular contractions. This means about 6 or more in 1 hour, even after you have had a glass of water and are resting.
- Not feeling well. This may include:
- Having a fever that you can't explain.
- Feeling unusually tired.
- Feeling pain in your belly when you press on it.
It is sometimes hard to tell the difference between Braxton Hicks contractions and preterm labor contractions.
You may have one or more of these symptoms and not be in preterm labor. But if you are concerned, talk to your doctor or nurse-midwife.
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.
A baby born too early may have complications, such as bleeding in the brain or chronic lung disease. The earlier a baby is born, the higher the risk.
Your doctors can prepare you for what may lie ahead. They can base this on your condition and how many weeks pregnant you will be when you give birth.
Thanks to improved medical care, more premature infants are surviving today than in years past. For more information, see the topic Premature Infant.
What Increases Your Risk
A risk factor is anything that increases your chances of having a problem.
Risk factors related to your pregnancy
- Pregnancy with twins, triplets, or more.
- Infection in the urinary or reproductive tract, including the vagina.
- Shortened cervix or incompetent cervix.
Risk factors related to your medical history
- A past preterm delivery.
- Previous surgery on your cervix, such as a cone biopsy. Having a loop electrosurgical excision procedure (LEEP) also may increase preterm labor risk.footnote 2 But experts don't know for sure if the increased risk is from the surgery itself or the problems with the cervix that led to surgery.footnote 3
Other risk factors
- Being younger than 18 years.
- Cigarette smoking during pregnancy.
- Use of cocaine or methamphetamine.
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. Use kick counting 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.
Who to see
If you are in preterm labor, you may be seen by:
- An obstetrician.
- A perinatologist, also known as a maternal-fetal medicine specialist.
- A family medicine doctor.
Exams and Tests
If you have symptoms of preterm labor, both you and your baby will be examined and monitored.
Information from these exams and tests can help you and your doctor or nurse-midwife decide whether to treat early labor and delay the birth or let it continue.
For the mother
You will be examined for tenderness in your uterus. Your temperature, pulse, and rate of breathing will be checked. Depending on your symptoms, you may have one or more exams or tests, including:
- Vaginal smear. This test looks for:
- Infection. Having an infection in the vagina can cause infection in your uterus. And that can trigger preterm labor as well as serious infection in the newborn.
- Amniotic fluid. Finding this fluid in the vagina means that your water has broken.
- Fetal fibronectin. When the test is negative, it is unlikely that you are having preterm labor. This test isn't used in all labor and delivery units.
- Vaginal exam. You'll be checked to see if the contractions have begun to open (dilate) or thin (efface) your cervix.
- Ultrasound to check the length of your cervix.
- Other tests for infection, such as a blood test, urine test, and urine culture.
For the baby
Preterm labor isn't always treated. When deciding whether—and how—to treat it, your doctor or nurse-midwife will think about:
- Your baby's weight and age. Ideally, preterm labor is delayed until a baby is mature enough to avoid problems after birth. When a pregnancy is nearing term (about 37 or more weeks), preterm labor is usually allowed to continue until delivery.
- Your health. Very high blood pressure, severe preeclampsia, HELLP syndrome, chronic disease, infection, or heavy bleeding can make it necessary to deliver right away.
- Your baby's health. Signs of fetal distress or illness can make it necessary to deliver right away.
- The stage of your labor and how fast it's moving along. For example, when your cervix is well effaced and dilated, medicine to slow labor is less likely to work.
- The distance to the nearest neonatal intensive care unit (NICU). If there is a good chance that you could be taken to the NICU, your doctor may try to slow labor.
If your water hasn't broken, you will be observed for at least an hour or two to see if your contractions continue and your cervix changes (opens and thins). If your cervix doesn't change, or if your contractions stop or slow down, you may be sent home.
If your cervix changes, you will be admitted to the labor and delivery unit.
In the hospital, your doctor or nurse-midwife may use medicines to:
- Slow or stop contractions.
- Treat infection.
- Help the baby's lungs mature.
- Help protect your baby's brain. If you're less than 32 weeks pregnant, your doctor or nurse-midwife may give you medicine to help prevent some problems that affect your baby's brain, such as cerebral palsy.footnote 4
For more information, see Medications.
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 and getting enough folic acid— 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 weekly progesterone shots during your second and third trimesters. Research shows that these shots may help lower your risk of preterm labor.footnote 3
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. Research has not shown that progesterone shots prevent preterm birth in women pregnant with more than one baby.footnote 4
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 or juice. Not having enough liquids can cause contractions.
- Stop what you are doing, and empty your bladder. Then lie down 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.
- Try to remember what you were doing when the symptoms started so that you can avoid starting the contractions again later.
Although stress isn't thought to be a direct cause of preterm labor, do what you can to reduce stress in your life. Try to do less, ask for help, and eat well.
Strict bed rest is no longer used to prevent preterm labor. But your doctor may recommend expectant management, which may involve some bed rest.
If your contractions are causing changes in your cervix, or if you have signs of infection or preterm premature 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.
- 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).
It isn't used to treat preterm labor. But for a woman who has had a preterm birth in the past because her cervix didn't stay closed, cervical cerclage may prevent another preterm birth.footnote 1
- Haas DM (2011). Preterm birth, search date June 2010. BMJ Clinical Evidence. Available online: http://www.clinicalevidence.com.
- Samson SA, et al. (2005). The effect of loop electrosurgical excision procedure on future pregnancy outcomes. Obstetrics and Gynecology, 105(2): 325–332.
- American College of Obstetricians and Gynecologists (2012). Prediction and prevention of preterm birth. ACOG Practice Bulletin No. 130. Obstetrics and Gynecology, 120(4): 964–973.
- American College of Obstetricians and Gynecologists (2012). Management of preterm labor. ACOG Practice Bulletin No. 127. Obstetrics and Gynecology, 119(6): 1308–1317.
Other Works Consulted
- American College of Obstetricians and Gynecologists (2007, reaffirmed 2012). Premature rupture of membranes. ACOG Practice Bulletin No. 80. Obstetrics and Gynecology, 109(4): 1007–1019.
- McDonald S, et al. (2005). Perinatal outcomes of in vitro fertilization twins: A systematic review and meta-analyses. American Journal of Obstetrics and Gynecology, 193: 141–152.
- Murphy KE, et al. (2008). Multiple courses of antenatal corticosteroids for preterm birth (MACS): A randomised controlled trial. Lancet, 372(9656): 2143–2151.
- Simhan HN, et al. (2014). Preterm labor and birth. In RK Creasy et al., eds., Creasy and Resnik's Maternal-Fetal Medicine, 7th ed., pp. 624–653. Philadelphia: Saunders.
- U.S. Preventive Services Task Force (2008). Screening for Bacterial Vaginosis in Pregnancy to Prevent Preterm Delivery: Recommendation Statement. Available online: http://www.uspreventiveservicestaskforce.org/uspstf08/bv/bvrs.htm.
- Yost NP, et al. (2006). Effect of coitus on recurrent preterm birth. Obstetrics and Gynecology, 107(4): 793–797.
Current as ofSeptember 5, 2018
Author: Healthwise Staff
Medical Review: Sarah A. 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, Reproductive Endocrinology
Current as of: September 5, 2018
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