Most pregnancies (about 90% of them) last until at least week 37 of pregnancy, but some babies are unexpectedly born a little sooner. Going into labor prematurely doesn’t necessarily mean you’ll give birth early. Preterm labor sometimes stops on its own, and certain treatments can also help slow things down.[1]
But because preterm birth can be harmful to babies, it’s important to know the signs of early labor and let your doctor know ASAP if you’re experiencing them. That way, your medical team can take steps to reduce any risk of pregnancy complications.
Here’s why premature labor can happen — and what you can do to help prevent it.
What is preterm labor?
The American College of Obstetricians and Gynecologists (ACOG) defines preterm labor as labor that occurs before week 37 of pregnancy. The latest research from the March of Dimes found that about 10% of moms see their expected nine months of pregnancy turn into an unexpected seven or eight months because they go into labor early.[2]
If your baby is born before your due date (or your doctor tells you you’re experiencing early labor), you’ll likely hear some of the terms below. Previously, a pregnancy was considered “full term” if it lasted between 37 and 42 weeks, but leading expert groups like ACOG adjusted these definitions a few years back. Now, a full-term pregnancy is defined as 39 weeks; and even though any birth is “preterm” before week 37, there are various definitions for how early a baby arrives:
- Late preterm: Baby is born between weeks 34 and 36.
- Moderately preterm: Baby is born between weeks 32 and 34 weeks.
- Very preterm: Baby is born before 32 weeks.
- Extremely preterm: Baby is born before 25 weeks.
Premature babies haven’t had as much time to develop and grow in your womb, so they’re more likely than full-term babies to have health conditions that need to be monitored and cared for longer in the hospital.
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What causes preterm labor?
Preterm labor is sometimes caused by a condition such as preeclampsia, a disorder that generally develops after week 20 and is characterized by a sudden onset of high blood pressure during pregnancy. Other times, early labor can happen spontaneously and seemingly for no reason at all.
The following factors might boost the risk of going into labor prematurely, but remember that you won't necessarily have to deal with preterm labor if one or more of these apply to you:
- Smoking, alcohol, and drug use: Not only do these increase your risk of miscarriage, they also up your baby’s risk of being born early or at a low birth weight. That's because toxins that cross the placenta can keep your little one from getting the necessary oxygen she needs to grow. If there’s ever a reason to quit, pregnancy is it.
- Uterine and vaginal infections: Infections — those in the genital tract, such as bacterial vaginosis (BV) and sexually transmitted diseases (STDs) like trichomoniasis, along with infections in the uterus or amniotic fluid — can be responsible for a preterm birth. Experts suspect they cause inflammation, which in turn leads to the release of prostaglandins — the same substance that initiates labor when you're full-term. Untreated urinary-tract infections during pregnancy can have the same effect, so let your OB/GYN know if you notice a burning sensation when you pee.
- Pregnancy complications: Certain complications (such as gestational diabetes) as well as problems with the placenta (placenta previa or placental abruption, for example) can make an early delivery more likely.
- Structural anomalies of the uterus and/or cervix: A uterus that is extremely large or has other structural abnormalities can make it more difficult to carry a baby to term, as can problems with the cervix (such as having a short cervix or cervical insufficiency when the cervix doesn't stay closed the way it's supposed to during pregnancy).
- Gum infections: Pregnancy hormones make expectant moms more susceptible to periodontal disease, which is important to have treated since it’s been linked to preterm labor. Some experts suspect that the bacteria that cause inflammation in the gums can actually get into the mom’s bloodstream, reach the fetus, and trigger early delivery.
- Occupational factors: Extreme physical stress on the job has also been linked to preterm labor. Researchers have found that women who have very long working hours or jobs that are extremely physically exhausting are more likely to deliver early.
- Carrying multiples: Multiples are more likely than singletons to arrive early.
- Maternal age: Women younger than 17 and older than 35 are more likely to deliver prematurely.
- A previous preterm birth: If you’ve given birth early previously, you’re at an increased risk of having a subsequent preterm birth, according to ACOG.
- If you were preterm yourself. One large study[3] found that women who were born prematurely themselves are at a higher risk of giving birth prematurely (though those odds are still low, at 14.2% or fewer, depending on how early you were born).
Preterm labor is also one of a number of pregnancy complications that disproportionately affect Black moms. Even though overall preterm birth rates declined in 2022, according to the Centers for Disease Control and Prevention (CDC), preterm birth among Black women was about 50% higher than it was for white women — 14.6% versus 9.4%.[4]
Signs of preterm labor
Preterm labor can be scary, but know that many women who have symptoms don’t end up delivering early. So while you hopefully won’t have to put this knowledge to use, it's good to have in your back pocket: The earlier you recognize that you're in labor, the earlier you'll be able to seek treatment.
Call your practitioner right away if you are experiencing these labor signs:
- Regular contractions: That is, those that come every 10 minutes (or more often) and do not subside when you change position (try lying down on your side). These are not to be confused with Braxton Hicks contractions that you've possibly already begun to feel, which are practice contractions that are no cause for concern (they’re irregular, don't intensify, and subside when you change position). If you're not sure, call your practitioner anyway.
- Change in vaginal discharge: Look for blood-streaked discharge (“bloody show”) or vaginal bleeding.
- Fluid leaking from your vagina: It could be a sign your water has broken. Take a sniff test: If it smells like ammonia, it's urine. If it doesn't, it could be amniotic fluid.
- Period-like cramps: Strong cramps you feel in your lower abdomen or lower back could be a sign of labor.
- Back pain: A constant low, dull back pain may be a sign of labor.
- Increased pelvic pressure: If you feel a significant increase in pressure in your pelvic area, call your doctor.
Keep in mind that you can have some of these symptoms and not be in labor (most pregnant women experience pelvic pain and pressure or lower back pain at some point, for example). But only your practitioner can tell for sure, so don’t hesitate to pick up the phone and call if you’re ever concerned about symptoms you’re experiencing.
Is there anything you can do to prevent preterm labor?
While medical advances have made it possible to successfully treat even the tiniest of premature babies, medical interventions to prevent preterm labor have been elusive, in large part because doctors still don't understand it enough to be able to develop effective ways to treat it.
And while preterm labor can sometimes start for seemingly no reason at all, there are steps you can take to minimize your chances. Even if you're not at risk of preterm labor (and especially if you are), there are ways to help encourage your baby to stay put until she’s completely ready for a healthy and timely arrival:
- See your doctor. Getting early and regular prenatal care can help your OB/GYN pinpoint and address any risk factors for preterm labor you might have, ensuring you have the healthiest pregnancy possible.
- Control what you can. Smoking, drinking, using drugs not prescribed by your doctor, or having untreated diabetes can all lead to preterm labor.
- Take your prenatal vitamins. A daily prenatal supplement enhances your overall health, improving the odds that you'll carry to term. In fact, research suggests that folic acid (which already does so much good for your baby) may also lower the risk of preeclampsia, which is responsible for a good percentage of early deliveries.[5]
- Eat well. Getting all the nutrients your body needs from a balanced pregnancy diet not only results in a healthier baby, but might also help her arrive at the right time. Adequate intake of certain omega-3 fatty acids (found in salmon, DHA eggs, walnuts and flaxseed) has been shown to reduce preterm labor (and boosts your baby's brain development).[6] Other studies have shown that vitamin C (citrus, berries, bell peppers) and calcium (milk and other dairy products or fortified juices) may also be helpful in preventing preterm labor.
- Stay hydrated. Drinking enough water (more if you're exercising or it's very hot) is good for you and your baby during pregnancy. And staying hydrated increases your odds of keeping baby put, since dehydration can lead to premature contractions.
- Be good to your gums. Preventative dental care is one of your first (and best, and easiest) lines of defense in preventing preterm labor, since it may be triggered by gum disease. So brush, floss and visit your dentist at least once during your pregnancy — not just for your regular cleaning, but also to take care of any little problems before they become big ones.
- Go when you gotta go. Not going when you gotta go could lead to a urinary tract infection, another cause of preterm contractions. So make a habit of peeing when you've got the urge to go.
- Treat it. If you're considered high-risk because you have BV or another infection, ask your practitioner if an oral antibiotic is right for you. Some studies show that symptomatic women with BV who are treated with antibiotics have a reduced risk of preterm delivery. Other studies, though, have disputed those findings, saying that there is no reduction in the rate of premature delivery even if the infection (both BV and other STDs) is treated. Your practitioner will be able to guide you.
Screenings for preterm labor risk
Unfortunately, there are no universal screening tests for preterm labor risk. But for high-risk patients, cervical length measurement between 16 and 22 weeks may be useful in predicting whether you're at risk of preterm birth.
If there are any signs that your cervix is shortening or opening, your practitioner may take some steps to prevent early labor — such as prescribing vaginal progesterone or perhaps stitching your cervix closed, called cerclage, according to ACOG.
What to expect if you experience preterm labor
If you're experiencing any symptoms of preterm labor, your practitioner will want to assess you — either in the office or the hospital. Here’s what to expect:
Tests for preterm labor: You'll first be hooked up to a fetal monitor to check for contractions and make sure your baby is not in any distress. Your cervix will be examined to determine if any dilation or effacement has begun, and your practitioner will probably use a vaginal swab to test for signs of infection and possibly fetal fibronectin. You might also receive an ultrasound to assess the amount of amniotic fluid and to confirm the size and gestational age of your baby. If these tests and exams show that you aren’t in labor, you'll be sent home, often with instructions to take it easy.
If your practitioner thinks you're in preterm labor: Because each day a baby remains in the womb improves the chances of survival and good health, your doctor’s main goal will be holding off labor for as long as possible. Or, depending on how far along in the pregnancy you are and what other complications you may be having, they may admit you to the hospital, where you might receive any or all of the following:
- Intravenous fluids: The better hydrated you are, the lower the chances of continued contractions.
- Antibiotics: You may receive antibiotics, especially if infection is believed to have triggered labor. And if you haven't yet been tested for Group B strep (the test is usually performed after 35 weeks), you'll be given IV antibiotics to prevent possible transmission of the bacteria to your baby in case you are indeed a carrier.
- Tocolytic agents: Your doctor may give you medications (like magnesium sulfate) to relax the uterus and, in theory, temporarily stop contractions. These are usually only dispensed if you're fewer than 32 weeks pregnant and at risk of immediate delivery.
- Corticosteroids: If your baby's lungs are still underdeveloped, you’ll receive these medications to speed up fetal lung maturity. Doctors have long advised that women between 24 and 34 weeks pregnant who are expected to go into imminent preterm labor have corticosteroids administered. In 2017, ACOG issued new recommendations suggesting that certain women at risk of preterm birth also be given antenatal corticosteroids during the late preterm birth period, or between 34 and 37 weeks of pregnancy. ACOG also says that women could consider starting the corticosteroid treatment at 23 weeks if they're at risk of a preterm delivery within seven days. The drugs help fast-track the growth of the fetus' lungs two to seven days after they're taken, boosting the chances that baby will successfully function and thrive without help outside the womb.
If at any point your practitioner determines that the risk to you or your baby outweighs the risk of preterm birth, they will not attempt to postpone delivery. The good news is that for about 30% of women, preterm labor stops on its own, ACOG says, and only about 10% of women who go into preterm labor give birth within the next seven days.[7]
Your premature baby's health
Premature babies often need to stay in the neonatal intensive care unit (NICU) for the first few days, weeks or, in some cases, months of their lives.
That’s because babies born early may have more health problems than babies born closer to their due dates. They may have anemia (when a baby doesn’t have enough blood cells to carry oxygen). They may also have breathing problems, infection, newborn jaundice, intestinal issues, and central nervous system complications. Little ones who arrive before 34 weeks are more likely to have health challenges, according to the March of Dimes.
Babies born between 34 and 37 weeks of gestation who have no other health problems generally do fine — and often only need a short stay in the NICU before they head home.
Whenever she arrives, rest assured that the latest medical advances mean even the earliest little ones have very good chances of surviving and thriving.
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