Uterine Contractions (Preterm Labor)

What is Uterine Contractions (Preterm Labor)?

Preterm labor occurs when regular uterine contractions cause the cervix to dilate and efface before 37 weeks of gestation. These contractions may feel like menstrual cramps, a tightening sensation in the abdomen, or a “wave” of pressure that comes and goes. While occasional Braxton‑Hicks “practice” contractions are normal throughout pregnancy, preterm uterine contractions are persistent, become increasingly painful, and are often accompanied by cervical changes.

Preterm birth is the leading cause of neonatal morbidity and mortality worldwide. According to the World Health Organization (WHO), about 15 million babies are born prematurely each year, and many of these births could be averted with early detection and timely treatment of preterm labor.¹

Common Causes

Most cases of preterm labor are multifactorial, but certain conditions increase the risk dramatically. Below are 10 of the most frequently identified contributors:

• Infection or inflammation – urinary tract infections, bacterial vaginosis, chorioamnionitis, or periodontal disease.
• Multiple gestation – twins, triplets, or higher-order multiples stretch the uterus.
• Cervical insufficiency – a weak or shortened cervix that cannot stay closed.
• Previous preterm birth – a history of delivering before 37 weeks raises recurrence risk.
• Maternal chronic conditions – hypertension, diabetes, autoimmune disease, or clotting disorders.
• Placental problems – placenta previa, abruption, or accreta.
• Uterine anomalies – bicornuate uterus, septate uterus, or fibroids.
• Substance use – tobacco, alcohol, illicit drugs, or excessive caffeine.
• Stress and physical trauma – severe emotional stress, domestic violence, or a fall.
• Low socioeconomic factors – inadequate prenatal care, poor nutrition, or limited access to health services.

Identifying the underlying cause helps guide therapy and informs counseling for future pregnancies.

Associated Symptoms

The presence of uterine contractions alone does not always mean labor is underway. Clinicians look for accompanying signs that suggest the cervix is changing:

• Regular, rhythmic contractions occurring every 5–10 minutes and lasting 30–70 seconds
• Low‑back or pelvic pain that may radiate to the thighs
• Vaginal discharge that is watery, mucus‑like, or tinged with blood (often called “bloody show”)
• Pressure feeling in the pelvis or a sensation that the baby is "dropping"
• Flank or abdominal pain not related to the uterus (may indicate kidney infection)
• Fever, chills, or other signs of infection
• Changes in fetal movement (decreased activity can be a warning sign)

When to See a Doctor

Because preterm labor can progress quickly, timely medical evaluation is essential. Contact a health professional if you notice any of the following:

• Contractions that are regular (every 5–10 minutes) and last longer than 30 seconds
• Any vaginal bleeding, spotting, or unusual discharge
• Persistent low‑back or pelvic pain that does not improve with rest
• Fever ≥ 100.4 °F (38 °C) or chills
• Sudden gush of fluid (possible rupture of membranes)
• Signs of infection such as burning with urination or foul‑smelling discharge

Even if you are unsure, it is safer to call your obstetrician, midwife, or go to the nearest labor & delivery unit. Early treatment can stop or delay labor and improve outcomes for both mother and baby.²

Diagnosis

Once you seek care, the clinician will use a combination of history, physical exam, and diagnostic testing:

1. Pregnancy History and Physical Examination

• Detailed review of symptoms, prior preterm births, infections, and risk factors.
• Measurement of uterine tone and palpation for tenderness.
• Speculum examination to assess cervical dilation, effacement, and any discharge.

2. Cervical Assessment

• Digital cervical exam – only performed if the provider suspects imminent labor; otherwise, an exam may be deferred to avoid triggering contractions.
• Transvaginal ultrasound – measures cervical length; a length < 25 mm before 24 weeks is a strong predictor of preterm birth.³

3. Contraction Monitoring

• External tocogram (tocodynamometer) or intrauterine pressure catheter to record frequency, duration, and intensity.

4. Laboratory Tests

• Urinalysis and urine culture – screen for urinary infection.
• Vaginal swab for bacterial vaginosis, yeast, or Group B Streptococcus.
• Complete blood count (CBC) – detect infection or anemia.
• Blood cultures if fever is present.
• Fetal fibronectin (fFN) test – a protein that, when present in cervicovaginal fluid between 22–34 weeks, indicates a higher risk of delivery within 7–14 days.⁴

5. Fetal Assessment

• Non‑stress test (NST) or biophysical profile (BPP) to evaluate fetal heart rate patterns and well‑being.
• Ultrasound for fetal growth, amniotic fluid volume, and placental position.

Treatment Options

Treatment aims to halt labor, treat underlying causes, and support fetal development. Management is individualized based on gestational age, severity of contractions, and presence of risk factors.

1. Medications to Stop or Slow Contractions

• Tocolytics – medications such as nifedipine (Calcium channel blocker), atosiban (oxytocin receptor antagonist), or indomethacin (NSAID, used only before 32 weeks). They buy time (generally 48 hours) for other interventions.
• Beta‑agonists (e.g., terbutaline) – less commonly used due to maternal side effects.

2. Corticosteroids for Fetal Lung Maturity

Betamethasone or dexamethasone given in two doses 24 hours apart is standard for pregnancies between 24–34 weeks. These drugs reduce the risk of neonatal respiratory distress syndrome, intraventricular hemorrhage, and neonatal death.⁵

3. Antibiotics

• Administered for confirmed infections (e.g., urinary tract infection, bacterial vaginosis, chorioamnionitis).
• Screen‑and‑treat for Group B Streptococcus if labor is imminent.

4. Magnesium Sulfate

Given when preterm delivery is likely before 32 weeks to protect the newborn’s brain and reduce the risk of cerebral palsy.⁶

5. Progesterone Supplementation

• Weekly intramuscular 17‑hydroxyprogesterone caproate or vaginal micronized progesterone for women with a history of prior preterm birth or a short cervical length.

6. Cervical Cerclage

In cases of cervical insufficiency (often diagnosed via ultrasound), a stitch (cerclage) is placed around the cervix to keep it closed, typically between 12–14 weeks or later if shortening is noted.

7. Lifestyle & Home Measures (Adjunctive)

• Strict pelvic rest – avoid intercourse, heavy lifting, and prolonged standing.
• Hydration – dehydration can provoke Braxton‑Hicks and true contractions.
• Stress reduction – relaxation techniques, guided breathing, and adequate sleep.
• Monitor contraction patterns at home using a paper chart or a smartphone app (if advised by clinician).

Prevention Tips

While not all cases are preventable, adopting healthy habits and receiving proper prenatal care can markedly lower risk:

• Early and regular prenatal visits – allow detection of cervical shortening, infection, or other red flags.
• Screen and treat infections promptly (urinary, vaginal, oral).
• Maintain a balanced diet rich in protein, iron, calcium, and omega‑3 fatty acids; consider prenatal vitamins with folic acid.
• Avoid smoking, alcohol, and illicit drugs – all are linked to preterm labor.
• Stay hydrated – aim for at least 8 glasses of water daily.
• Exercise safely – low‑impact activities (walking, prenatal yoga) improve circulation; avoid high‑intensity or contact sports.
• Manage chronic conditions (e.g., keep blood pressure and blood glucose under control).
• Progesterone therapy if you have a prior early preterm birth or a short cervix, as recommended by your provider.
• Stress management – counseling, meditation, or support groups can reduce cortisol spikes that have been linked to uterine activity.

Emergency Warning Signs

If you experience any of the following, seek emergency care immediately (call 911 or go to the nearest emergency department):

• Regular, painful contractions occurring every 5 minutes or less, lasting longer than 1 minute
• Sudden gush or continuous leaking of fluid (possible rupture of membranes)
• Heavy vaginal bleeding (soaking a pad in minutes) or clots larger than a golf ball
• Severe abdominal pain that does not improve with rest
• Fever of 100.4 °F (38 °C) or higher with chills
• Rapid swelling of the face, hands, or feet combined with shortness of breath (possible pre‑eclampsia)
• Decreased fetal movement (less than 10 movements in 2 hours) after 28 weeks

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References:

1. World Health Organization. Preterm birth. WHO Fact Sheet, 2023.
2. Mayo Clinic. Preterm labor and birth. Updated 2024.
3. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin No. 235: Cervical Length Measurement and Prediction of Preterm Birth. 2022.
4. National Institutes of Health. Fetal Fibronectin Testing for Prediction of Preterm Delivery. 2021.
5. National Institute for Health and Care Excellence (NICE). Preterm labour and birth: management. NG25, 2022.
6. American Academy of Pediatrics. Magnesium Sulfate for Neuroprotection in Preterm Infants. 2023.