What is Preterm labor?
Preterm labor (also called premature labor) is the onset of regular uterine contractions that cause the cervix to dilate and efface before 37 weeks of gestation. A pregnancy that reaches 37 weeks or later is considered full‑term; therefore, any birth that occurs earlier is classified as preterm. Preterm labor can lead to a preterm birth, which is a major cause of neonatal morbidity and mortality worldwide.
Most women who experience preterm labor will deliver a baby before the expected due date, but the exact timing varies. Some may go into true labor and deliver within hours, while others may have “false labor” (uterine activity without cervical change) that resolves with treatment.
According to the CDC, approximately 10 % of births in the United States are preterm, making it an important public‑health issue.
Common Causes
Preterm labor is usually multifactorial. The following conditions are most frequently linked to early uterine activation:
- Infection or inflammation – urinary tract infections, bacterial vaginosis, chorioamnionitis, and systemic infections can trigger cytokine release that stimulates uterine contractions.
- Multiple gestation – twins, triplets, or higher-order multiples stretch the uterus more than a singleton pregnancy.
- Cervical insufficiency – a weak or short cervix can dilate under the weight of the growing fetus.
- Placental problems – placental abruption, previa, or insufficiency may cause bleeding and uterine irritation.
- Maternal chronic conditions – hypertension, diabetes, autoimmune disorders (e.g., lupus), and thyroid disease increase risk.
- Maternal lifestyle factors – smoking, illicit drug use (cocaine, methamphetamines), excessive alcohol, and poor nutrition.
- Uterine anomalies – fibroids, congenital uterine malformations, or a previous uterine surgery (e.g., myomectomy) can affect uterine contractility.
- Physical trauma – falls, motor‑vehicle accidents, or direct abdominal injury.
- Stress and psychosocial factors – chronic emotional stress, intimate partner violence, or severe anxiety have been linked to earlier labor.
- Short inter‑pregnancy interval – becoming pregnant less than six months after a previous delivery.
Associated Symptoms
The hallmark of preterm labor is regular uterine contractions, but many other symptoms often appear together:
- Lower‑back or abdominal cramping that feels similar to menstrual cramps
- Feeling of pressure in the pelvis or a “ball‑like” sensation
- Vaginal discharge that is watery, mucous‑like, or tinged with blood (sometimes called “bloody show”)
- Low‑grade fever (≥100.4 °F or 38 °C) or chills, especially if infection is present
- Change in fetal movement – a noticeable decrease may signal distress
- Gastro‑intestinal upset such as nausea, vomiting, or diarrhea
- Urinary urgency or burning if a urinary tract infection is the trigger
When to See a Doctor
Preterm labor can develop quickly. Seek medical care immediately if you notice any of the following:
- Regular contractions (every 5–10 minutes) lasting longer than an hour
- Any vaginal bleeding, spotting, or brown discharge
- Clear fluid leaking from the vagina (possible rupture of membranes)
- Persistent lower‑back pain that does not improve with rest
- Fever ≥100.4 °F (38 °C) without an obvious cause
- Sudden, severe abdominal pain
- Decreased fetal movement (fewer than 10 movements in 2 hours)
Even if you have only one symptom (e.g., a small amount of fluid loss), contacting your obstetric provider is advisable because early evaluation can prevent a full‑blown preterm birth.
Diagnosis
When you arrive at the clinic or emergency department, the care team will use several tools to determine whether you are in true preterm labor:
1. History and Physical Examination
- Detailed questions about the pattern of contractions, vaginal discharge, bleeding, and recent infections.
- Abdominal palpation to feel for uterine tenderness.
2. Cervical Assessment
- Digital cervical exam – evaluating dilation, effacement, and consistency (softening).
- Transvaginal ultrasound – measures cervical length; a length <25 mm before 24 weeks is a strong predictor of preterm birth.
3. Monitoring Contractions
- External tocodynamometer (wrist monitor) or an intrauterine pressure catheter for more precise measurement.
4. Laboratory Tests
- Urinalysis and urine culture (rule out UTI)
- Vaginal swab for bacterial vaginosis, Trichomonas, or Group B Streptococcus
- Blood tests: CBC (look for infection), CRP, blood type, and Rh factor
- If membranes are suspected to be ruptured: nitrazine paper test or ferning test on vaginal fluid.
5. Fetal Well‑Being Assessment
- Non‑stress test (NST) or biophysical profile (BPP) to evaluate heart rate patterns and movement.
Treatment Options
Treatment aims to (1) stop the labor process, (2) treat any underlying cause, and (3) improve fetal maturity. The approach varies with gestational age, severity of symptoms, and the presence of contraindications.
Medical Interventions
- Tocolytics – medications that relax the uterus. Common agents include:
- nifedipine (Calcium‑channel blocker) – first‑line for most patients
- atosiban (oxytocin receptor antagonist) – used in Europe and Canada
- indomethacin (NSAID) – effective before 32 weeks but avoided later due to fetal renal effects
- terbutaline (β‑agonist) – reserved for short‑term use because of maternal side‑effects
- Corticosteroids – betamethasone 12 mg IM x2 doses 24 h apart, or dexamethasone 6 mg IM q12 h ×4 doses, given between 24‑34 weeks to accelerate fetal lung maturity.
- Antibiotics – indicated if infection is identified (e.g., ampicillin‑gentamicin for chorioamnionitis) or for prophylaxis in women with preterm premature rupture of membranes (PPROM).
- Magnesium sulfate – administered when delivery <32 weeks is anticipated to protect the infant’s brain and reduce cerebral palsy risk.
- Progesterone supplementation – 17‑hydroxyprogesterone caproate weekly injection or vaginal progesterone gel for women with a history of preterm birth or a short cervix.
Hospital‑Based Supportive Care
- Continuous fetal monitoring and bedside ultrasound to track cervical change.
- IV fluid hydration to maintain uterine perfusion.
- Bed rest (often limited to observation in a labor‑and‑delivery unit); prolonged strict bed rest is no longer routinely recommended.
Home‑Based Measures (when appropriate)
- Pelvic rest – avoid intercourse, douching, and digital cervical examinations.
- Hydration – drink at least 2–3 L of water per day unless fluid‑restricted for another condition.
- Stress reduction – gentle breathing exercises, guided meditation, or prenatal yoga (with physician approval).
- Prompt treatment of urinary or vaginal infections under physician guidance.
Prevention Tips
While not all cases of preterm labor can be prevented, several evidence‑based strategies reduce risk:
- Early prenatal care – regular visits allow prompt detection of infections, cervical shortening, and other risk factors.
- Screen and treat infections – urine cultures each trimester; treat bacterial vaginosis if symptomatic.
- Progesterone therapy for women with a prior preterm birth or a cervical length ≤25 mm (as recommended by ACOG).
- Healthy lifestyle – quit smoking, avoid illicit drugs, limit caffeine, and maintain a balanced diet rich in fruits, vegetables, whole grains, and lean protein.
- Weight management – aim for a BMI within the normal range before conception; excessive weight gain can increase risk.
- Vaccinations – flu and Tdap (tetanus, diphtheria, pertussis) protect both mother and baby from infections that may precipitate labor.
- Avoid harmful exposures – limit exposure to environmental pollutants, heavy metals, and occupational hazards.
- Stress reduction – seek counseling, join support groups, and practice relaxation techniques.
- Spacing pregnancies – wait at least 18–24 months after a birth before trying again.
Emergency Warning Signs
If any of the following occur, call 911 or go to the nearest emergency department immediately:
- Heavy vaginal bleeding (soaking a pad in <10 minutes) or large clots
- Sudden, intense abdominal or pelvic pain that does not subside with rest
- Clear fluid leaking continuously (possible rupture of membranes)
- Fever ≥ 100.4 °F (38 °C) with chills, indicating possible infection
- Rapidly increasing contractions (every 2–3 minutes) that do not stop with hydration or rest
- Severe headache, vision changes, or swelling (possible preeclampsia, which can trigger preterm labor)
- Decreased fetal movements (fewer than 10 kicks in 2 hours)
**References**
- Mayo Clinic. “Preterm labor.” Mayoclinic.org. Accessed May 2026.
- Centers for Disease Control and Prevention. “Preterm Birth.” CDC.gov. Updated 2024.
- American College of Obstetricians and Gynecologists. “Committee Opinion No. 818: Cervical Length Screening and Progesterone to Prevent Preterm Birth.” 2020.
- National Institutes of Health. “Preterm Birth.” NIH NICHD.
- World Health Organization. “Preterm birth.” WHO Fact Sheet, 2022.
- Cleveland Clinic. “Preterm Labor: Symptoms, Causes, and Treatment.” 2023.