Preterm labour symptoms

Preterm labour symptoms are regular painful uterine contractions occurring between viability and 37 weeks of gestation. Other symptoms are pelvic pressure, backache, menstrual like cramps, increased vaginal discharge, watery or bloodstained loss, or a sense that the baby is pushing down.

The main clinical points are:

• Separate true preterm labour (regular contractions with progressive cervical change) from irritability of the uterus that settles.
• Identify and treat causes such as infection and bleeding.
• Give corticosteroids and magnesium sulphate in time.
• Transfer the woman to a unit with neonatal intensive care before birth.
• Avoid both missed labour and unnecessary admission.

Clinical relevance. Preterm birth is the leading cause of neonatal death and long term disability in children. Antenatal corticosteroids, magnesium sulphate for neuroprotection, delayed cord clamping and transfer to a suitable unit before birth improve outcomes substantially.

Physiology. Painless uterine activity (Braxton Hicks contractions) occurs throughout pregnancy and rises in the third trimester. True labour has regular contractions that increase in strength and frequency, with cervical effacement and dilatation. The cervix normally measures over 30 mm at 18 to 32 weeks.

Mechanisms. Preterm labour follows premature activation of the mechanisms of parturition. Triggers include intrauterine infection or inflammation, decidual haemorrhage (abruption), uterine overdistension (multiple pregnancy, polyhydramnios), cervical insufficiency, stress and uterine anomalies. Many cases have no cause identified.

Classification.

• By gestation: extremely preterm (under 28 weeks), very preterm (28 to under 32 weeks), moderately preterm (32 to under 34 weeks) and late preterm (34 to under 37 weeks).
• By status: threatened preterm labour (symptoms without cervical change), established preterm labour (regular contractions with cervical dilatation of 4 cm or more), and preterm prelabour rupture of membranes with contractions.

Key distinctions. Contractions alone do not establish labour. Cervical change, a short cervix, ruptured membranes, bleeding or a positive biomarker do. Painless cervical shortening (cervical insufficiency) can present with pressure and discharge. Symptoms with fever, uterine tenderness or foul discharge suggest intra amniotic infection.

History

• Gestation (confirmed by earliest scan) and plurality.
• Symptoms: frequency and regularity of contractions, pain pattern, backache, pelvic pressure, watery loss (ruptured membranes), bleeding, mucous plug or show, foetal movements, urinary symptoms, fever, diarrhoea.
• Risk factors, obstetric: previous preterm birth or late miscarriage (strongest), multiple pregnancy, short cervix, previous cervical surgery (cone biopsy, large loop excision), uterine anomaly, fibroids, polyhydramnios.
• Risk factors, infection: bacterial vaginosis and other infections, urinary tract infection, periodontal disease.
• Risk factors, lifestyle and other: smoking, cocaine and other drug use, extremes of maternal age, short interval between pregnancies, low body mass index, assisted conception, bleeding in pregnancy, abdominal trauma, intimate partner violence, heavy physical work and stress.
• Medical: diabetes, hypertension, renal disease, thyroid disease, sickle cell disease, HIV, malaria, syphilis, anaemia.
• Obstetric: previous caesarean section (scar), cerclage, previous labour course, rhesus status.
• Social: access to hospital, distance, transport.

Examination

• Maternal vital signs (temperature, pulse, blood pressure, respiratory rate), hydration.
• Abdomen: uterine tenderness, tone, contractions palpated over 10 minutes, fundal height, lie, presentation, foetal heart.
• Sterile speculum examination first: pooling of fluid, visible cervical dilatation, bleeding, cord or membranes at the os, discharge, infection. Obtain swabs and biomarker samples before any digital examination.
• Digital vaginal examination only if the membranes are intact, placenta praevia is excluded and the woman is contracting regularly: dilatation, effacement, station, presentation, membranes.
• Cardiotocography and tocography from viability.
• Bedside tests: urine dipstick (nitrites, leucocytes, blood, protein, ketones), capillary glucose.

Red flags

• Regular contractions with cervical dilatation of 3 cm or more, or visible membranes.
• Rupture of membranes, especially with fever, uterine tenderness or foul liquor.
• Vaginal bleeding or constant abdominal pain (abruption).
• Fever, maternal or foetal tachycardia (intra amniotic infection).
• Abnormal cardiotocography, reduced foetal movements.
• Hypertension, headache or epigastric pain (pre eclampsia).
• Breech presentation, cord prolapse, transverse lie.
• Multiple pregnancy, previous preterm birth, cervical length under 25 mm.
• Severe abdominal pain with systemic illness (appendicitis, pyelonephritis).
• Gestation under 24 weeks (periviable), or no access to a neonatal unit.

Special groups. Multiple pregnancy: earlier intervention and higher risk. Women with cerclage: signs of failure. HIV infection: continue antiretroviral therapy and plan prevention of mother to child transmission. Sickle cell disease: pain crisis may mimic contractions. Region specific: malaria, syphilis and untreated bacterial vaginosis contribute to preterm birth. Delay in transfer is a leading cause of neonatal death.

Organised by cause of the symptoms. Each cause is common unless marked serious or uncommon.

Uterine causes of contractions

• Braxton Hicks contractions and uterine irritability (the commonest cause of premature contractions).
• True preterm labour (idiopathic, spontaneous).
• Cervical insufficiency (painless cervical shortening and dilatation).
• Serious: placental abruption.
• Serious: intra amniotic infection (chorioamnionitis).
• Preterm prelabour rupture of membranes.
• Uterine fibroids with degeneration or distortion.
• Uterine anomaly (septate, bicornuate), uterine overdistension (multiple pregnancy, polyhydramnios).
• Serious: uterine rupture (after previous caesarean section or surgery).

Infection and inflammation

• Urinary tract infection, asymptomatic bacteriuria and pyelonephritis.
• Bacterial vaginosis, trichomoniasis, chlamydial and gonococcal infection, syphilis.
• Group B streptococcus colonisation or infection, listeriosis.
• Malaria, influenza, COVID-19 and other systemic infection with fever.
• Periodontal disease.

Abdominal and surgical causes

• Appendicitis, cholecystitis, pancreatitis, bowel obstruction.
• Gastroenteritis, constipation, irritable bowel syndrome, renal colic.
• Ovarian torsion or cyst accident, adnexal pathology.
• Round ligament pain, pelvic girdle pain, symphysis pubis dysfunction.
• Abdominal trauma and domestic abuse.

Other causes

• Dehydration, intercourse (prostaglandins in semen), cocaine and drug use.
• Pre eclampsia and HELLP syndrome, sickle cell crisis.
• Early term labour mistaken for preterm labour because of dating error.
• Foetal anomaly or demise with uterine activity.

Stepwise reasoning

1. Confirm gestation and plurality, and assess maternal and foetal condition (cardiotocography, tocography).
2. Perform a sterile speculum examination, take swabs, and assess for rupture of membranes and bleeding.
3. Assess the cervix: digital examination when the woman is contracting regularly and membranes are intact; otherwise use transvaginal cervical length and biomarkers.
4. Estimate the probability of birth within 7 days using cervical length, foetal fibronectin or placental alpha microglobulin 1 where available (or a validated risk tool).
5. Decide on admission, corticosteroids, magnesium sulphate, tocolysis and transfer.

First line tests

• Cardiotocography and tocography (at least 30 minutes).
• Urine dipstick and culture; midstream sample before antibiotics.
• High vaginal swab for bacterial vaginosis, trichomonas and candida; nucleic acid amplification tests for chlamydia and gonorrhoea; low vaginal and rectal swab for group B streptococcus.
• Full blood count, C reactive protein (a rising or raised value supports infection; steroid administration also raises white cell counts), group and screen, urea, creatinine, electrolytes.
• Ultrasound: presentation, liquor volume, growth, placental site and abruption, cervical length.
• Blood glucose or HbA1c if risk.
• Malaria test, syphilis serology and HIV test where indicated.

Cervical assessment

• Transvaginal cervical length: 30 mm or more makes birth within 7 days unlikely, and the woman can usually be discharged; under 15 mm indicates high risk and is an indication for admission and full preterm labour care; 15 to 29 mm needs a second test.
• Foetal fibronectin (quantitative or qualitative): a negative result (under 10 ng/mL on the quantitative test) makes birth within 7 to 14 days very unlikely; a positive test has modest predictive value. It is invalid after intercourse, digital examination, bleeding or lubricant in the preceding 24 hours.
• Placental alpha microglobulin 1 and phosphorylated insulin like growth factor binding protein 1 tests are alternatives where available.
• Digital examination of the cervix in a woman with regular painful contractions: dilatation of 3 cm or more, effacement of 80% or more, and progressive change on repeat examination after 1 to 2 hours confirm labour.

Infection tests

• Intra amniotic infection: maternal temperature 38.0°C or more, with maternal tachycardia (over 100 beats/min), foetal tachycardia (over 160 beats/min), uterine tenderness or purulent liquor; raised C reactive protein and white cell count. Amniocentesis (glucose, culture, interleukin 6) is rarely used.

Targeted tests

• Ultrasound for fibroids, uterine anomaly and funnelling of the cervix.
• Doppler and growth ultrasound when growth restriction is suspected.
• Kleihauer test for rhesus negative women with bleeding.
• Toxicology screen if drug use is suspected.

Limitations. Contractions are not specific. Digital examination is subjective and may introduce infection. Cervical length and biomarkers are most useful in women with intact membranes and symptoms between 24 and 34 weeks. A negative test does not remove the need for safety netting. Foetal fibronectin is unreliable after bleeding or recent examination.

Immediate steps. Admit women with regular contractions and cervical change, ruptured membranes, bleeding, abnormal cardiotocography or high risk. Call the obstetric and neonatal teams.

Check the unit's neonatal capacity for the gestation. If the unit cannot provide care, arrange in utero transfer before birth if time allows. Transfer is not safe in advanced labour. Give oxygen if hypoxic and intravenous fluids if dehydrated. Treat fever and infection.

Antenatal corticosteroids.

• Betamethasone 12 mg intramuscularly, two doses 24 hours apart (or dexamethasone 6 mg intramuscularly every 12 hours for four doses).
• Give from 24 weeks to 34 weeks and 6 days when birth is expected within 7 days.
• Consider from 22 to 23 weeks after counselling, and up to 36 weeks and 6 days on specialist advice.
• A single repeat (rescue) course may be given if the first course was more than 7 to 14 days before and the woman is again at risk before 34 weeks.
• In diabetes, monitor glucose closely for 48 to 72 hours and adjust insulin.
• Do not delay transfer for steroids.

Magnesium sulphate for neuroprotection. For imminent birth before 30 weeks (and up to 34 weeks in some services): 4 g intravenously over 15 to 30 minutes, then 1 g/h until birth or for a maximum of 24 hours.

Monitor respiratory rate (over 12 breaths/min), oxygen saturation, patellar reflexes and urine output (over 0.5 mL/kg/h). In renal impairment reduce the dose and check levels. Antidote: calcium gluconate 10% 10 mL (1 g) intravenously over 10 minutes. Avoid with myasthenia gravis.

Tocolysis (to delay birth by 48 hours for steroids and transfer, not to prolong pregnancy)

• Consider between 24 and 33 weeks and 6 days with intact membranes, no contraindication, and no evidence of infection or compromise.
• Nifedipine (first line): 20 mg orally as a loading dose, then 10 to 20 mg orally every 6 to 8 hours for up to 48 hours (maximum 160 mg daily). Monitor blood pressure and pulse. Headache, flushing and tachycardia are common.
• Avoid nifedipine in hypotension, aortic stenosis and severe hepatic impairment. Use caution with magnesium sulphate and in multiple pregnancy.
• Atosiban (alternative where available): 6.75 mg intravenously bolus over 1 minute, then 300 microgram/min infusion for 3 hours, then 100 microgram/min for up to 45 hours (maximum duration 48 hours, total dose 330 mg). It has fewer maternal side effects.
• Indomethacin 50 to 100 mg rectally, then 25 mg orally or rectally every 6 hours for up to 48 hours, only before 32 weeks (risk of ductus arteriosus constriction and oligohydramnios).
• Indomethacin is contraindicated in renal impairment, peptic ulcer, asthma sensitive to NSAIDs and bleeding disorders.
• Avoid beta agonists (terbutaline, ritodrine), which cause maternal pulmonary oedema, arrhythmia and metabolic effects. Do not use magnesium sulphate as a tocolytic. Maintenance tocolysis is not effective.
• Contraindications to tocolysis: abruption, chorioamnionitis, severe pre eclampsia or eclampsia, foetal compromise, lethal anomaly or foetal death, advanced labour (cervix 4 cm or more with rapid progress), maternal instability, and rupture of membranes with infection.

Antibiotics. Not given routinely to women with intact membranes and preterm labour, since they do not delay birth. Treat identified infection.

• Asymptomatic bacteriuria and urinary tract infection, by culture: cefalexin 500 mg orally every 12 hours for 5 to 7 days.
• Bacterial vaginosis: metronidazole 400 mg orally twice daily for 5 to 7 days.
• Chlamydia: azithromycin 1 g orally once.
• Gonorrhoea: ceftriaxone 1 g intramuscularly once.
• Syphilis: benzathine benzylpenicillin 2.4 million units intramuscularly weekly for 3 weeks for late latent disease, or once for early disease.
• Malaria: by species.

Intrapartum group B streptococcus prophylaxis. Give in established labour (or ruptured membranes) when the swab is positive, status is unknown, or there was group B streptococcus bacteriuria or a previous affected baby.

• Benzylpenicillin 3 g (5 million units) intravenously, then 1.5 g every 4 hours until birth.
• Alternative: ampicillin 2 g, then 1 g every 4 hours.
• Penicillin allergy at low risk of anaphylaxis: cefazolin 2 g intravenously, then 1 g every 8 hours.
• High risk allergy: clindamycin 900 mg intravenously every 8 hours (if the isolate is susceptible) or vancomycin 20 mg/kg intravenously every 8 hours (maximum 2 g a dose).

Intra amniotic infection.

• Ampicillin 2 g intravenously every 6 hours with gentamicin 5 mg/kg intravenously once daily (adjusted to renal function).
• After caesarean birth, add metronidazole 500 mg intravenously every 8 hours (or clindamycin 900 mg intravenously every 8 hours).
• Paracetamol 1 g every 4 to 6 hours (maximum 4 g daily).
• Deliver irrespective of gestation. Continue antibiotics until the woman has been afebrile for 24 hours.

Mode and conduct of birth. Continuous foetal monitoring. Choose the mode by presentation and foetal condition. Caesarean section for breech presentation is debated before 28 weeks and individualised. Avoid vacuum extraction before 34 weeks. Delay cord clamping for 30 to 60 seconds in vigorous infants (longer in some services). Have a neonatal resuscitation team present. Early skin to skin contact when stable.

Periviable gestation (22 to 25 weeks). Joint counselling by obstetric and neonatal consultants about survival and disability, using local outcome data. Decisions about resuscitation, caesarean section and steroids reflect parental wishes and the baby's condition.

Women discharged after assessment (not in labour). Cervical length 30 mm or more, or negative biomarker, no cervical change, normal cardiotocography, intact membranes and a reachable hospital. Give written safety netting and a follow up date within 1 week. Treat any infection.

Prevention in future pregnancies

• Vaginal micronised progesterone 200 mg nightly (or 90 mg gel daily) from 16 to 24 weeks until 34 to 36 weeks for women with a short cervix (under 25 mm) found at the mid pregnancy scan, or previous spontaneous preterm birth.
• Cervical cerclage, history indicated: at 12 to 14 weeks for three or more previous second trimester losses or preterm births.
• Cervical cerclage, ultrasound indicated: when cervical length is under 25 mm before 24 weeks and there is a previous preterm birth or loss.
• Rescue cerclage for advanced dilatation with intact membranes in selected women, with indomethacin and antibiotics.
• Arabin pessary is an alternative with limited evidence.
• Serial cervical length scans every 2 weeks from 16 to 24 weeks for high risk women.
• Eradicate asymptomatic bacteriuria and treat symptomatic infection.
• Screen and treat bacterial vaginosis in women with a previous preterm birth.
• Stop smoking. Allow a birth interval of 18 months or more.
• Low dose aspirin 75 to 150 mg from 12 weeks for those at risk of pre eclampsia.
• Hydroxyprogesterone caproate injections are not advised because evidence of benefit is lacking.

Special groups.

• Multiple pregnancy: progesterone is not effective. Use cervical length scans and early steroids. Cerclage is not advised without a short cervix.
• Sickle cell disease: hydration, oxygen and analgesia.
• HIV: continue antiretroviral therapy and plan caesarean section if viral load is not suppressed.
• Region specific: antenatal steroids are safe and effective in settings with adequate neonatal care, but not in settings without it for late preterm infants. Give antibiotics for rupture of membranes, kangaroo mother care for low birthweight infants, and ensure transport.

Monitoring. Contractions, maternal temperature, pulse and blood pressure every 4 hours (hourly with tocolysis). Cardiotocography every 4 to 6 hours (continuous in active labour). Tocolysis monitoring and fluid balance. Repeat cervical assessment after 2 to 4 hours if symptoms continue.

Referral and escalation. Refer to the unit with neonatal intensive care for any woman under 34 weeks with established labour or rupture of membranes. Call the neonatal team early. Refer to a foetal medicine specialist for a short cervix, previous preterm birth, or multiple pregnancy. Refer to anaesthesia for planning of analgesia.

Admission criteria. Regular contractions with cervical change, ruptured membranes, bleeding, positive biomarker with symptoms, cervical length under 15 mm, abnormal cardiotocography, maternal illness, multiple pregnancy with symptoms, or inability to return quickly.

Discharge and follow up. Discharge once contractions have settled, cervical length or biomarker is reassuring, the foetal state is normal and a follow up plan is in place. Antenatal review in 1 week, and cervical length surveillance when risk is high.

Safety netting. Return at once for regular contractions, waters breaking, bleeding, constant pain, reduced foetal movements, fever, offensive discharge or pelvic pressure.