Most pregnancies (or about 90 percent of them, roughly speaking) last to term — which is at least week 37 of pregnancy (though that's now called "early term"; full-term babies are born between 39 weeks of pregnancy and week 40 of pregnancy). But sometimes, baby unexpectedly arrives sooner. Here’s why premature labor happens — and what you can do to help prevent it.
What is considered preterm labor?
Preterm, or premature, labor occurs after week 20 of pregnancy and before week 37.
The latest research from the March of Dimes shows that the number of cases of premature labor is on the rise for the fifth year in a row, and around 10 percent of moms find their expected nine months of pregnancy turns into an unexpected seven or eight because they go into labor too soon.
What might cause preterm labor?
While no one knows for sure what causes preterm labor, experts point to a number of factors that could play a role in triggering your uterus to begin contracting and your cervix dilating before your baby is ready to come out:
- Smoking, alcohol and drug use: Not only do these increase your risk of miscarriage, they also increase your baby’s risk of being born early or at a low birth weight (toxins that cross the placenta can keep your baby from getting the necessary oxygen she needs to grow). If there’s ever a reason to quit, pregnancy is it.
- Short interval between pregnancies: Getting pregnant sooner than 18 months after giving birth to your last child increases your risk of preterm birth. And the longer you can wait, the less you’re at risk: A large recent study found that 20 percent of women who wait less than a year between pregnancies give birth before 37 weeks; the rate drops to 10 percent among women who wait a year to 18 months and is less than 8 percent in those who wait more than 18 months to conceive again.
- Uterine and vaginal infections: Infections — both those in the genital tract, such as bacterial vaginosis (BV) and sexually transmitted diseases (STDs) like trichomoniasis, along with infections in the uterus and amniotic fluid — are thought to be responsible for nearly half of all preterm births. 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 can have the same effect.
- Pregnancy complications: Complications (such as gestational diabetes, preeclampsia and excessive amniotic fluid) as well as problems with the placenta (such as placenta previa or placental abruption) 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 cervical length or an incompetent cervix — 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 in turn has been linked to preterm labor. Some experts suspect that the bacteria that cause inflammation in the gums can actually get into mom’s bloodstream, reach the fetus and initiate early delivery. Other research proposes another possibility: The bacteria that cause inflammation in the gums can also trigger the immune system to produce inflammation in the cervix and uterus, triggering early labor.
- Stress levels: Researchers theorize that severe emotional stress — not the kind caused by those raging hormones or a bad day, but the kind that's related to a traumatic experience — can lead to the release of hormones that in turn trigger labor contractions.
- Occupational factors: Extreme physical stress on the job has also been linked to preterm labor. Researchers have found that women who stand for long periods of time (more than five hours a day) or who have 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 than their younger counterparts 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.
- If you were preterm yourself. A large 2015 study 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 percent or less depending on how early you were born).
Most important to remember, however, is that having one of these risk factors doesn't mean that you'll necessarily go into preterm labor. Similarly, not having any of the risk factors doesn't mean that you won't (some women do for other reasons — or for no known reason at all).
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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.
But that doesn't mean there's nothing you as a concerned mom-to-be can do. Even if you're not at risk for preterm labor (and especially if you are), there are plenty of ways to help keep your baby put until he or she is completely ready for a healthy and timely arrival:
- Aim for 18 months between pregnancies. Your rate of preterm labor drops significantly if you wait at least a year — and optimally 18 months — between when you last gave birth and when you conceive again.
- See your doctor. Getting early and regular prenatal care can help your doctor pinpoint and help you treat any risk factors for preterm labor and ensure 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. Eliminate any that apply to you.
- 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 placental abruption (the placenta separating from the uterine wall) and preeclampsia, two conditions that are responsible for a good percentage of early deliveries.
- Eat well. Getting all the nutrients your body needs from a healthy, balanced pregnancy diet not only results in a healthier baby but also one that arrives at the right time. Adequate intake of certain omega-3 fatty acids (found in salmon, DHA eggs, walnuts and flax seed) has been shown to reduce preterm labor (and boosts your baby's brain development). Other studies have shown that vitamin C (citrus, berries, bell peppers) and calcium (milk and other dairy products or fortified juices) can also be helpful in preventing preterm labor.
- Eat often. Research suggests that it's not enough to ship your baby all the right nutrients — you should also make those shipments as regular as possible. Pregnant women who eat at least five times a day (three meals and two snacks, or five smaller meals, for instance) are less likely to deliver prematurely.
- Drink up. Drinking enough water (more if you're exercising or it's very hot) will keep you hydrated. 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 can 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. Holding in your urine, besides being uncomfortable, can inflame your bladder — which in turn could irritate your uterus and set off contractions. Not going when you gotta go could also 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, 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.
- Explore your options. If you've already had one preterm labor, recent research has found that the hormone progesterone (given as a shot or a gel during weeks 16 through 36) reduces the risk for preterm birth in women with a prior history — so ask your practitioner if it might help 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 to 22 weeks may be useful in predicting whether you're at risk for 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 putting you on bed rest, prescribing vaginal progesterone or perhaps stitching your cervix closed, called cerclage.
How to recognize preterm labor
A full 80 percent of women who have symptoms of preterm labor will not deliver early. And while it's likely you'll never 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 or all of these symptoms and not be in labor (most pregnant women experience pelvic pain/pressure or lower back pain at some point). But only your practitioner can tell for sure, so pick up the phone and call. After all, better safe than sorry.
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 to make sure the 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 — or perhaps to go on modified bed rest.
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. He or she may put you on bed rest. Or, depending on how far along in the pregnancy you are and what other complications you may be having, she may admit you to the hospital, where you may 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 less than 34 weeks pregnant and if your baby's lungs are deemed too immature for 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, the American College of Obstetricians and Gynecologists (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, he or she will not attempt to postpone delivery. The good news is that for about 30 percent of women, preterm labor stops on its own, and only about 10 percent of women who go into preterm labor give birth within the next seven days.
Your premature baby's health
A baby born before 34 weeks will almost always need to stay in the neonatal intensive care unit (NICU) for the first few days, weeks or, in some cases, months of his or her life.
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.
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