Preterm Labor: Warning Signs Every Mom Should Know

Preterm labor — labor that begins before 37 weeks of pregnancy — is a scenario no expectant parent wants to face, but one that every pregnant woman should understand. According to the CDC, approximately 1 in 10 babies in the United States is born prematurely, making preterm birth the leading cause of infant morbidity and mortality in the developed world.

Knowing the warning signs of preterm labor can be the difference between a baby born at 26 weeks with months of NICU care ahead and a baby who makes it to 34 or 36 weeks with far fewer complications. Every day a baby remains in the womb matters — particularly between weeks 24 and 34. Review our third trimester guide for the full picture of what happens in these critical weeks, when lung development and brain maturation are progressing rapidly.

This guide covers the warning signs you need to recognize, the risk factors that increase your chances, what happens if preterm labor is diagnosed, and what modern medicine can do to give your baby the best possible start.

📌 Key Takeaway: Preterm labor occurs before 37 weeks. Warning signs include regular contractions, pelvic pressure, lower back pain, vaginal discharge changes, and cramping. If you suspect preterm labor, call your provider immediately — treatments like tocolytics and antenatal steroids can delay delivery and improve outcomes. Knowing the signs and acting quickly is the most important thing you can do. Also review the differences between Braxton Hicks and real contractions to avoid confusion.

What Is Preterm Labor?

Preterm labor is defined as regular contractions that cause cervical dilation (opening) or effacement (thinning) before 37 weeks of gestation. It’s important to distinguish between:

• Preterm labor — Contractions with cervical change before 37 weeks (a medical condition requiring intervention)
• Preterm birth — Actual delivery before 37 weeks (the outcome if preterm labor cannot be stopped)
• Threatened preterm labor — Contractions without significant cervical change (may resolve on its own)

ACOG classifies preterm birth into subcategories based on gestational age:

📊 Key Data: According to the March of Dimes, the U.S. preterm birth rate was approximately 10.4% in 2022. Late preterm births (34–36 weeks) account for the largest proportion and generally have good outcomes with appropriate care. Extremely preterm births carry the highest risk but survival rates have improved dramatically with advances in neonatal medicine.

Warning Signs of Preterm Labor

Recognizing the signs of preterm labor early is critical. If you experience any of the following symptoms before 37 weeks, contact your healthcare provider immediately:

1. Regular Contractions (More Than 4 Per Hour)

Contractions that occur at regular intervals — every 10–15 minutes or more frequently — and do not stop with rest, hydration, or position changes may indicate preterm labor. These may feel like:

• Tightening across the abdomen
• Menstrual-like cramping that comes and goes
• A rhythmic “balling up” of the uterus

Use our Contraction Timer to track the frequency and duration of contractions.

2. Persistent Lower Back Pain

A dull, constant ache in the lower back that doesn’t improve with rest or position changes — particularly if it’s rhythmic or coincides with abdominal tightening.

3. Pelvic Pressure

A feeling of heaviness or pressure in the pelvis, as if the baby is pushing down. This is different from the normal third-trimester pelvic discomfort — it’s more intense and persistent.

4. Abdominal Cramping

Menstrual-like cramps, with or without diarrhea. These may be constant or come and go in waves.

5. Change in Vaginal Discharge

An increase in vaginal discharge, a change in its consistency (watery, mucus-like, or bloody), or the passage of the mucus plug before 37 weeks.

6. Vaginal Bleeding or Spotting

Any vaginal bleeding in the second or third trimester should be reported to your provider. Light spotting can be benign, but bleeding combined with other symptoms is a red flag.

7. Fluid Leaking from the Vagina

A gush or steady trickle of fluid may indicate premature rupture of membranes (PPROM). This requires immediate medical evaluation due to infection risk.

⚠️ Important: Do not wait to see if symptoms resolve on their own. Call your healthcare provider or go to labor and delivery immediately if you experience any combination of these symptoms before 37 weeks. Early intervention can delay delivery by days or even weeks — and every additional day in the womb improves your baby’s chances.

Risk Factors

While preterm labor can happen to anyone, certain factors increase the risk.

What to Do If You Suspect Preterm Labor

If you’re experiencing warning signs before 37 weeks:

1. Call your provider immediately — Describe your symptoms, including contraction timing
2. Lie down on your left side — This improves blood flow to the uterus
3. Drink water — Dehydration can trigger contractions; drink 2–3 glasses
4. Empty your bladder — A full bladder can stimulate uterine contractions
5. Time your contractions — Note frequency, duration, and intensity using our Contraction Timer
6. Do not take any medications unless directed by your provider
7. Go to the hospital if your provider advises or if symptoms worsen

Track your pregnancy week and milestones with our Pregnancy Week Tracker.

Treatments for Preterm Labor

If preterm labor is confirmed (regular contractions with cervical change), your medical team has several interventions available.

Tocolytics (Contraction-Stopping Medications)

Tocolytics are medications that slow or stop contractions to buy time — typically 48 hours — for other critical treatments to take effect. They are not intended to stop preterm labor permanently.

Common tocolytics include:

• Magnesium sulfate — Also provides neuroprotection for the baby’s brain
• Nifedipine — A calcium channel blocker that relaxes uterine muscle
• Indomethacin — An anti-inflammatory, used primarily before 32 weeks
• Terbutaline — A beta-agonist, used short-term only

Antenatal Corticosteroids

This is arguably the most important intervention for preterm babies. A course of corticosteroids (typically betamethasone — two injections given 24 hours apart) accelerates fetal lung maturation. According to ACOG, antenatal steroids are recommended for all pregnant women between 24 and 33 weeks 6 days who are at risk of delivery within 7 days.

The benefits are substantial:

• Reduces respiratory distress syndrome (RDS) by approximately 50%
• Reduces intraventricular hemorrhage (brain bleeding) by approximately 50%
• Reduces necrotizing enterocolitis (intestinal complication) by approximately 50%
• Reduces neonatal mortality by approximately 30%

Magnesium Sulfate for Neuroprotection

When delivery before 32 weeks appears imminent, ACOG recommends magnesium sulfate infusion for the mother. This treatment has been shown to reduce the risk of cerebral palsy in the baby by approximately 30–40%.

Antibiotics

If premature rupture of membranes (PPROM) occurs, antibiotics are given to prevent infection and delay delivery. Antibiotics can extend the pregnancy by an average of 7–10 days, which can be critical for fetal development.

NICU Survival Rates by Gestational Week

Modern neonatal intensive care has dramatically improved outcomes for premature babies. The following table provides general survival rates — actual outcomes depend on birth weight, gender (girls tend to do slightly better), the hospital’s NICU level, and individual medical factors.

📊 Key Data: According to a study published in the New England Journal of Medicine, survival rates for babies born at 24–27 weeks have improved by approximately 15–20 percentage points over the past two decades, largely due to advances in antenatal steroid use, surfactant therapy, and neonatal ventilation techniques.

Prevention Strategies

While not all preterm births are preventable, evidence-based strategies can reduce risk:

1. Progesterone supplementation — For women with a history of preterm birth, vaginal progesterone (starting at 16–24 weeks) can reduce recurrence risk by approximately 30%, per ACOG.
2. Cervical cerclage — A stitch placed in the cervix for women with cervical insufficiency or a short cervix. Typically placed between weeks 12 and 14.
3. Cervical length screening — Transvaginal ultrasound to measure cervical length between weeks 16 and 24. A cervix shorter than 25 mm may warrant progesterone or cerclage.
4. Smoking cessation — Quitting smoking reduces preterm birth risk and improves overall pregnancy outcomes.
5. Infection treatment — Prompt treatment of urinary tract infections, bacterial vaginosis, and other infections reduces preterm risk.
6. Adequate prenatal care — Regular prenatal visits allow early detection of risk factors.
7. Pregnancy spacing — Waiting at least 18 months between pregnancies reduces risk.
8. Stress management — Chronic stress is associated with preterm labor; relaxation techniques, adequate rest, and support are protective.

FAQ

Can preterm labor stop on its own?

Yes. Threatened preterm labor — contractions without significant cervical change — can sometimes resolve with rest, hydration, and monitoring. However, you should always be evaluated by your provider to determine whether cervical change is occurring. Even if contractions stop, your provider may recommend activity restrictions, cervical length monitoring, or progesterone supplementation.

What happens if my baby is born at 34 weeks?

Babies born at 34 weeks are considered “late preterm” and generally do well. Most have a short NICU stay (1–2 weeks) for feeding support, temperature regulation, and monitoring. They may initially have difficulty with breastfeeding and temperature control, but the vast majority go home healthy within a few weeks. Long-term outcomes for late preterm babies are excellent.

Does bed rest prevent preterm labor?

Current evidence does not support routine bed rest for preventing preterm labor. ACOG states that bed rest has not been shown to reduce preterm birth rates and may increase the risk of blood clots and muscle loss. Your provider may recommend activity modification (reduced physical exertion) rather than strict bed rest. Always follow your provider’s specific guidance for your situation.

Is preterm labor more common with twins?

Yes. Approximately 50% of twin pregnancies and over 90% of triplet pregnancies result in preterm delivery, according to the March of Dimes. The increased uterine distension from multiple babies is a primary factor. Women carrying multiples are monitored more closely for signs of preterm labor, and cervical length screening is typically performed more frequently.

References

• American College of Obstetricians and Gynecologists. “Preterm Labor and Birth.” acog.org
• Centers for Disease Control and Prevention. “Preterm Birth.” cdc.gov
• March of Dimes. “Preterm Labor and Premature Birth.” marchofdimes.org
• Mayo Clinic. “Preterm Labor.” mayoclinic.org
• Stoll BJ, et al. “Trends in Care Practices, Morbidity, and Mortality of Extremely Preterm Neonates.” JAMA. jamanetwork.com

Written by

Vega Lin

Founder & Editor — Mother of 2 (Taiwan)

Vega writes Pregnancy Guide from the intersection of evidence-based research (ACOG, CDC, WHO) and her own experience as a mother of two. Completing her Master's in Digital Innovation at Tunghai University. Read more →

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