About 10 percent of American babies are born prematurely. Find out more about the causes of preterm labor, which happens before 37 weeks of pregnancy, and learn how to distinguish the symptoms.

By Richard Schwarz, M.D., Lisa Milbrand, and Jeanne Faulkner, R.N.
Updated July 20, 2020
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Gajus/Shutterstockn
Gajus/Shutterstock

Preterm labor happens when a woman goes into labor before 37 weeks of pregnancy. According to March of Dimes, about 10 percent of babies are born prematurely in America. The majority are delivered between 34 and 36 weeks, and most of them are healthy and need little or no special care after birth. 

If a baby is born before 32 weeks, however, the prognosis is less optimistic. That’s because premature delivery can result in negative health consequences such as low birth weight, vision or breathing difficulties, improper organ development, and learning disabilities

Fortunately, though, if you’re at risk for preterm labor, your doctor might be able to prolong your pregnancy, which gives your baby more time to develop. Keep reading to learn more about the causes and symptoms of preterm labor, as well as the prevention methods your doctor might take.

Warning Signs of Preterm Labor

You're probably experiencing a whole range of new sensations throughout your pregnancy. So how can you tell if you’re feeling a simple stomach muscle cramp or a preterm contraction? Look for the following preterm labor symptoms and warning signs. 

The contractions feel different than Braxton Hicks.

After about 30 weeks of pregnancy, many women notice occasional uterine contractions. Called Braxton Hicks contractions, they're normal and usually painless. They tend to occur when you're tired or exerting yourself, and they usually stop when you rest. True premature contractions come at regular intervals or progressively become more frequent or more painful; Braxton Hicks contractions don't.

You feel a tightening in your belly at regular intervals.

Anytime you're feeling something happening at what seems like regular intervals, time them. "The contractions may be painless, but they'll be predictable," says Siobhan Kubesh, a certified midwife with OBGYN North in Austin. "If they seem to be coming every 10 minutes or [more frequently], and you can predict when they'll start and stop, you need to call your health care provider."

You have some spotting.

You may have some bleeding or discharge of bloody mucus if you're experiencing labor. "Any unexplained vaginal bleeding is a concern," Kubesh says. If the vaginal discharge changes, it's worth a quick call to your doctor.​

Your water breaks.

If you have a sudden gush of fluid—an indication that your water broke—you should call your doctor immediately.​

You feel something weighty in your pelvis.

"If there's a feeling of fullness in your vagina—if it feels like the baby's head is in the vagina—that's a symptom of preterm labor," Kubesh says.

Preterm Labor Risk Factors

Any pregnant woman can experience preterm labor. However, certain factors increase your risk, including:

  • History of preterm labor or premature birth
  • Pregnancy with multiples
  • Smoking, drinking alcohol, or using drugs
  • Being underweight or overweight
  • Maternal health problems like diabetes, preeclampsia, or high blood pressure
  • Problems with the placenta, cervix, or uterus
  • Certain maternal infections, including sexually transmitted diseases
  • Birth defects in the baby
  • Short interval between pregnancies (less than 12 months)
  • A shortened cervix

Some women at high risk for preterm labor are given a belt with electronic sensors, which is strapped around the abdomen to detect early contractions. Once or twice a day, the monitor is hooked up to a telephone so it can relay graphs of uterine activity to a nurse. The goal of home monitoring is to detect preterm labor early, when it's most treatable.

Diagnosing Preterm Labor 

You’re considered to be in preterm labor when you have uterine contractions every ten minutes (or more often) as well as cervical changes (dilation, thinning, softening) prior to 37 weeks gestation. Your doctor might have difficulty determining whether you’re truly in labor. They’ll probably tell you to go to the hospital (if you're not already there), where you can be monitored carefully. 

Two tests—one that measures hormones in the saliva and another that measures vaginal secretions—can aid in diagnosing preterm labor. Doctors may do a swab of the cervix and vagina to test for a protein called fetal fibronectin. The March of Dimes explains, "Fetal fibronectin (fFN) is a protein produced during pregnancy and functions as a biological glue, attaching the fetal sac to the uterine lining. The presence of fFN during weeks 24-34 of a high-risk pregnancy, along with symptoms of labor, suggests that the ‘glue’ may be disintegrating ahead of schedule and alerts doctors to a possibility of preterm delivery." A vaginal ultrasound, which can accurately assess cervical dilation and other cervical changes, may help too.

If your doctor determines that you are truly in labor, they’ll probably attempt to halt it, unless it's not advisable for a medical reason. (For instance, doctors might not stop preterm labor if they detect maternal high blood pressure, uterine bleeding because of a problem with the placenta, or fetal distress signals like a slowed heart rate.)

Early Labor Intervention: How to Handle Preterm Labor

In some cases, preterm labor can be treated to give your baby more time to grow. Your doctor will likely choose between natural and medicated approaches.

Preventing Preterm Labor Naturally

"The most common cause of preterm labor is dehydration or bladder infection, so rest and hydration can help it resolve on its own," Kubesh says. Pelvic rest—which means no sex, no vaginal exams, and nothing put into your vagina—is often a must if you're experiencing preterm contractions. In some cases, your doctor may suggest sewing your cervix shut (cervical cerclage) to help avoid a premature birth, or even resting with your head below the level of your body to further reduce stress on the cervix.

You may also be put on bed rest, at least temporarily, to avoid having gravity put pressure on your cervix.  "Bed rest is one of the few things that has been shown to help prevent preterm birth," says Bart Putterman, M.D., an OB-GYN at Texas Children's Pavilion for Women in Houston.

To try to halt your contractions, your doctor will ask you to rest on your left side (this position increases blood flow to the uterus), and if you seem dehydrated, she will give you intravenous fluids. These steps help stop contractions in about 50 percent of women. If your contractions stop and your cervix doesn't dilate during several hours of observation, you will probably be able to go home.

Preventing Preterm Labor with Medication

Your obstetrician may decide that postponing the birth through medication is the appropriate course of action. While there is no established "right" time to start treatment with medication, many doctors recommend beginning once your cervix becomes two to three centimeters dilated. These drugs don’t usually don't postpone labor for long (often not more than a couple of days), but sometimes even a short delay can make a lifesaving difference to your baby.

For example, your doctor can begin treatment with corticosteroid drugs between 24 and 34 weeks of pregnancy, which are aimed at preventing or lessening complications in preterm newborns. Corticosteroids speed maturation of fetal organs, reducing infant deaths by about 30 percent and cutting the incidence of the two most serious complications of preterm birth: respiratory distress syndrome and bleeding in the brain. They are given by injection and are most effective when administered at least 24 hours before delivery. Other medication options include magnesium sulfate (which might reduce the risk of cerebral palsy) and tocolytics (which temporarily slow contractions). 

It’s important to note, though, that preterm labor medications aren't completely harmless. "The medications can have dangerous side effects, especially when taken for an extended length of time," Dr. Putterman says. "We don't have a really good means for prolonging pregnancy, short of getting you off of your feet."

Will I Need to Deliver the Baby?

Your contractions are unlikely to stop on their own if your cervix is dilating. As long as you’re between 34 and 37 weeks and the baby already is at least 5 pounds, 8 ounces, the doctor may decide not to delay labor. These babies are very likely to do well even if they're born early.

If you have concerns about preterm contractions, speak with your doctor who can recommend strategies to help you safely get to 40 weeks.

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