Preterm Labor: Warning Signs, Causes, and Management

About 1 in 10 babies in the US is born before 37 weeks, making the country an outlier among high-income nations for preterm birth rates. Preterm labor is the entry point for most early births, and recognizing it quickly is the single most important thing you can do, because early evaluation opens up interventions that can either delay delivery or, when delivery is unavoidable, prepare the baby for life outside the uterus. The mechanisms behind preterm labor are still incompletely understood, but the practical steps to identify it are well established — and they start with knowing the warning signs and acting on them without delay.

This article is educational information, not medical advice, and it is not a substitute for care from your own obstetric team. If you think you may be in preterm labor, the guidance below is simple: contact your OB or go to labor and delivery now.

Warning Signs — and When to Seek Care Now

Symptoms of preterm labor can be subtle and easy to dismiss as normal pregnancy discomfort, which is exactly why they are dangerous. Before 37 weeks, treat any of the following as a reason to call your obstetric provider or go to labor and delivery triage promptly:

• Regular or frequent contractions — often felt as a tightening or hardening of the abdomen, especially more than four to six in an hour or coming every 10 minutes or less.
• Low, dull backache that comes and goes, or constant low back pressure.
• Pelvic or vaginal pressure — a feeling that the baby is pushing down.
• Menstrual-like cramps, with or without abdominal cramping or diarrhea.
• A change in vaginal discharge — especially a sudden increase, or discharge that becomes watery, mucus-like, or tinged with blood.
• A leak or gush of fluid from the vagina, which can mean your water has broken (rupture of membranes).
• Vaginal bleeding.
• A noticeable decrease in the baby’s movements.

Do not wait to see if the symptoms pass. Call your OB, midwife, or labor and delivery unit right away if you have regular contractions before 37 weeks, a leak or gush of fluid, vaginal bleeding, strong or increasing pelvic pressure, or reduced fetal movement. If you have heavy bleeding, severe pain, signs that your water has broken with the cord or a body part visible, or you feel faint, call 911 or go to the nearest emergency department. Early evaluation preserves treatment options; there is no downside to being checked and sent home reassured.

How is this different from normal pregnancy tightening? Braxton-Hicks contractions are typically irregular, not painful, and ease with rest or hydration. Preterm labor contractions tend to be regular, may grow longer, stronger, and closer together, and are often accompanied by cervical pressure or back pain. When in doubt, be checked — timing contractions and reporting them to your provider is the safest response.

What Preterm Labor Is

Preterm labor is regular uterine contractions accompanied by cervical change (dilation, effacement, or both) before 37 weeks of pregnancy. Preterm birth is delivery before 37 weeks. The categories matter clinically: extremely preterm (before 28 weeks), very preterm (28 to 32 weeks), and moderate-to-late preterm (32 to 37 weeks). About 70 percent of preterm births are late preterm.

Some preterm births are spontaneous (resulting from labor or premature membrane rupture); others are medically indicated for conditions like severe preeclampsia, intrauterine growth restriction, or placental abruption. Each pathway has different prevention strategies, which is one reason your care team tailors recommendations to your individual history rather than a one-size-fits-all plan.

Risk Factors

The strongest single risk factor is a prior preterm birth, with recurrence rates of roughly 15 to 30 percent depending on the gestational age of the prior delivery and the underlying cause. Multiple gestation (twins, triplets) carries high risk; about 60 percent of twins and almost all triplets deliver preterm.

Other risk factors include a short cervix on second-trimester ultrasound (less than 25 mm at 18 to 24 weeks), uterine anomalies, previous cervical surgery (LEEP, conization) or a history of cervical insufficiency, prior cesarean, infections including bacterial vaginosis and untreated urinary tract infections, smoking, illicit drug use, periodontal disease, low pre-pregnancy BMI, inadequate weight gain, significant physical or psychological stress, advanced maternal age (over 35), short interpregnancy interval (less than 6 months), first-trimester bleeding, and pregnancy conceived with IVF.

Importantly, many preterm births occur in people with no identifiable risk factors, so the absence of risk factors is not a guarantee. In the US, Black women experience preterm birth at rates roughly 50 percent higher than white women — a disparity that reflects structural healthcare inequities, chronic stress exposure, and other factors that medical interventions alone cannot fully address.

How Preterm Labor Is Evaluated

Evaluation typically includes assessment of the contraction pattern (often continuous monitoring for one to two hours), a sterile speculum exam to check for membrane rupture and cervical dilation, transvaginal ultrasound to measure cervical length, and tests for infection and, when relevant, group B strep. Fetal fibronectin (fFN), a glycoprotein, is sometimes tested in symptomatic women between 22 and 34 weeks; a negative result has a high negative predictive value, meaning preterm birth is unlikely in the next one to two weeks. A positive fFN is less specific and does not necessarily mean labor is imminent.

Cervical length less than 25 mm by transvaginal ultrasound between 18 and 24 weeks identifies higher risk in singleton pregnancies. Some practices screen everyone; others screen only those with risk factors. Your OB or a maternal-fetal medicine specialist interprets these tests together with your symptoms and history — no single test decides the plan on its own.

How Clinicians Manage Preterm Labor

Every treatment below is chosen, dosed, and monitored by your obstetric or maternal-fetal medicine team. None of it is self-administered, and the descriptions here are general education, not instructions. When preterm labor is confirmed, the goals are usually to delay delivery long enough to give the baby the benefit of corticosteroids, provide neuroprotection when appropriate, treat infection, and arrange care at a hospital with the right level of newborn support.

Antenatal corticosteroids. A short, clinician-directed course of a corticosteroid (betamethasone or dexamethasone) is commonly given between 24 and 34 weeks when preterm birth is anticipated. Corticosteroids help mature the baby’s lungs and reduce neonatal respiratory distress syndrome, intraventricular hemorrhage, and mortality, per ACOG. They may also be considered at 22 to 24 weeks if delivery is imminent and the family chooses active intervention, and selectively in the late preterm window (34 to 36 weeks) for people at high risk of imminent delivery. The specific regimen is determined by the care team.

Magnesium sulfate. When very preterm delivery (generally before 32 weeks) is expected, intravenous magnesium sulfate given in the hospital before birth is used for fetal neuroprotection and is associated with a lower risk of cerebral palsy in surviving infants.

Tocolytics. Medications that briefly delay delivery — typically for up to about 48 hours — include nifedipine (a calcium channel blocker), indomethacin (an NSAID, used before 32 weeks), and terbutaline (rarely used now because of maternal side effects). Tocolytics buy time for corticosteroids to take effect and for transfer to an appropriate hospital; they do not, by themselves, improve long-term pregnancy outcomes.

Antibiotics. If your water has broken preterm, or if you are group B strep positive or unknown and delivering, antibiotics may be used based on your clinical picture and current guidelines.

Prevention Strategies

For people with a prior spontaneous preterm birth, options include vaginal progesterone, often started in the second trimester. Cervical cerclage (a stitch placed in the cervix) is offered to some people with a prior preterm birth and a short cervix on ultrasound. Following the PROLONG trial, ACOG no longer recommends 17-OHP (Makena) for routine prevention, and the medication has since been withdrawn from the US market — a good example of why prevention plans should be confirmed with your current provider rather than older articles.

For people without a prior preterm birth but found to have a short cervix on routine ultrasound, vaginal progesterone reduces preterm birth risk. Cerclage is not generally recommended in this group in the absence of a prior preterm birth. Other measures with supporting evidence include treating asymptomatic bacteriuria, smoking cessation, treating periodontal disease, and consistent prenatal care.

What Early Birth Means for the Baby

Outcomes vary dramatically by gestational age at birth. Term infants (37 weeks and beyond) typically do well. Late preterm infants (34 to 36 weeks) generally do well but have higher rates of feeding difficulties, jaundice, transient breathing problems, and NICU stays compared with term infants.

Moderately preterm (32 to 33 weeks) infants usually need NICU care for breathing support and feeding maturity. Very preterm (28 to 31 weeks) infants face higher risks of respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, and longer-term developmental concerns. Extremely preterm (before 28 weeks) is the highest-risk category, with survival rates rising steadily over recent decades but with substantial neurodevelopmental risks for survivors.

Modern neonatal intensive care has dramatically improved outcomes at every gestational age. Survival at 22 to 23 weeks now occurs in some centers, though with high rates of significant disability among survivors. Counseling at the threshold of viability weighs family preferences, local outcomes data, and individual baby factors, and is handled by the neonatology and obstetric teams together with the family.

Frequently Asked Questions

Can preterm labor be stopped?

Often only briefly. Tocolytic medications can delay delivery by roughly 48 to 72 hours, which allows critical interventions like corticosteroids and magnesium sulfate and, when needed, transfer to a hospital with a higher-level NICU. Long-term continuation of pregnancy after true preterm labor is unusual; the most common course is delivery within one to seven days of the labor episode. This is another reason not to delay being evaluated — the window to act is short.

What is the earliest a baby can survive?

Survival has been documented as early as 21 to 22 weeks in tertiary care centers, with rates improving steadily. Outcomes at the threshold of viability remain highly variable, and decisions about active intervention typically involve detailed discussion between families and neonatology teams.

Can I prevent preterm labor in my next pregnancy?

People with a prior preterm birth should be evaluated by a maternal-fetal medicine specialist, ideally before or early in a subsequent pregnancy. Vaginal progesterone, cervical-length monitoring, and cerclage (when indicated) can reduce recurrence. Lifestyle measures — not smoking, treating infections, and consistent prenatal care — also help.

What does a short cervix mean?

A cervical length less than 25 mm on transvaginal ultrasound between 18 and 24 weeks indicates higher preterm birth risk. Vaginal progesterone reduces this risk. In people with a prior preterm birth and a short cervix, cerclage is also considered. Your provider will explain what your specific measurement means for your care.

Should I go in even if I’m not sure it’s real labor?

Yes. Clinicians expect to evaluate people who turn out not to be in preterm labor, and being reassured and sent home is a good outcome. If you are before 37 weeks and have any of the warning signs above, call your provider or go to labor and delivery — do not try to diagnose yourself at home.

The Bottom Line

Preterm labor is one of the most consequential events in pregnancy, and recognizing it early opens up the most options. The most useful thing you can carry away from this guide is the list of warning signs and a low threshold for calling your OB or going to labor and delivery before 37 weeks. Modern obstetrics has effective, clinician-directed tools — antenatal corticosteroids, magnesium sulfate, and the targeted use of progesterone and cerclage — that meaningfully change newborn outcomes when they are used at the right time. Getting checked promptly is what makes that timing possible.

Sources

• MedlinePlus (U.S. National Library of Medicine) — Preterm labor (warning signs, when to call, risk factors, evaluation, management)
• American College of Obstetricians and Gynecologists (ACOG) — Preterm (Premature) Labor and Birth
• Centers for Disease Control and Prevention (CDC) — Preterm Birth (US preterm birth rate and disparities)