Premature labour

Synonym: preterm labour

What is premature labour?

Infants born as a result of premature labour have significant morbidity as a result of immaturity. Accurate diagnosis of preterm labour can allow for the prevention or delay of preterm birth where possible and, where this is not possible, earlier provision can be made to provide optimal support for the immature infant.

How common is premature labour? (Epidemiology)¹

• Preterm birth is the single biggest cause of neonatal mortality and morbidity in the UK. Over 52,000 babies (around 7.3% of live births) in England and Wales in 2012 were born preterm (before 37+0 weeks of pregnancy). There has been no decline in the preterm birth rate in the UK over the last 10 years.

• Around 75% of preterm births occur after preterm labour, which may or may not be preceded by preterm prelabour rupture of membranes. The remaining women giving birth preterm have an elective preterm birth when this is thought to be in the fetal or maternal interest (eg, extreme growth restriction in the baby or maternal conditions such as pre-eclampsia).

Risk factors²

• Low socio-economic status.

• Black race.

• Low pre-pregnancy body mass index (19.8 or less).

• Mother's work physically strenuous.

• Cocaine or heroin use.

• Uterine anomalies.

• Medical disorders - eg, thyroid disease, diabetes mellitus, hypertension.

• Infections of urinary and genital tracts; sexually transmitted infections.

• Periodontal disease.

• History of abdominal surgery.

• History of cervical conisation or a loop electrosurgical excision procedure of cervical transformation zone.

• History of preterm delivery.

• Short pregnancy interval (less than 18 months between pregnancies).

• Multiple gestation pregnancy.

• Polyhydramnios or oligohydramnios.

• Shortened cervix (less than 25 mm before 28 weeks of gestation).

• Vaginal bleeding caused by placental abruption or placenta praevia.

Worldwide, the greatest risk factor is infection, mainly from malaria, HIV and mycoplasma.

Diagnosis of premature labour¹

Pregnant women may present with a history of painful contractions. Additional indications of preterm labour may be gained through history and examination.

History

• Length of time that the contractions have been experienced.

• Interval between contractions.

• Bleeding or amniotic fluid loss.

• Previous obstetric history - any previous preterm deliveries.

• History of current pregnancy - infections, bleeding, pain, single or multiple fetuses.

• Smoking history.

Examination

• Speculum examination may reveal dilatation of the cervix and/or amniotic fluid leak through the cervix.

• Digital examination:
  

  • This should not be performed if it is thought that the membranes have ruptured, as this will increase the risk of infection to the fetus.

  • If the membranes have not ruptured, however, vaginal examination should be performed, as it is the best way of assessing the onset of premature labour.

Women with intact membranes

The National Institute for Health and Care Excellence (NICE) recommends:

• Assess women reporting symptoms of preterm labour who have intact membranes, including speculum examination, followed by a digital vaginal examination if the extent of cervical dilatation cannot be assessed. If a swab for fetal fibronectin testing is anticipated, the swab should be taken before any digital vaginal examination.

• If assessment suggests suspected preterm labour and 29+6 weeks pregnant or less, advise treatment for preterm labour.

• If assessment suggests suspected preterm labour and 30+0 weeks pregnant or more, consider transvaginal ultrasound measurement of cervical length as a diagnostic test to determine likelihood of birth within 48 hours:

  • If cervical length more than 15 mm, unlikely to be preterm labour.

  • If cervical length 15 mm or less, diagnose preterm labour.

• Consider fetal fibronectin testing as a diagnostic test to determine likelihood of birth within 48 hours for women who are 30+0 weeks pregnant or more if transvaginal ultrasound measurement of cervical length is indicated, but is not available or not acceptable:

  • If fetal fibronectin negative (50 ng/ml or less), preterm labour unlikely.

  • If fetal fibronectin positive (more than 50 ng/ml), diagnose preterm labour.

• If suspected preterm labour and 30+0 weeks or more does not have transvaginal ultrasound measurement of cervical length or fetal fibronectin testing to exclude preterm labour, offer treatment consistent with preterm labour.

• Do not use transvaginal ultrasound measurement of cervical length and fetal fibronectin testing in combination to diagnose preterm labour.

Preterm prelabour rupture of membranes (P-PROM)

• If symptoms suggestive of P-PROM, offer a speculum examination to look for pooling of amniotic fluid and if pooling of amniotic fluid is observed, do not perform any diagnostic test but offer care consistent with the woman having P-PROM (see below).

• If pooling of amniotic fluid is not observed, perform an insulin-like growth factor binding protein-1 test or placental alpha-microglobulin-1 test of vaginal fluid.

• If the results of the insulin-like growth factor binding protein-1 or placental alpha-microglobulin-1 test are positive, do not use the test results alone to decide what care to offer the woman, but also consider clinical condition, medical and pregnancy history and gestational age, and either:

  • Offer care consistent with the woman having P-PROM (see below re antenatal prophylactic antibiotics, identifying infection in women and maternal corticosteroids); or

  • Re-evaluate the woman's diagnostic status at a later time point.

• If the results of the insulin-like growth factor binding protein-1 or placental alpha-microglobulin-1 test are negative and no amniotic fluid is observed, do not offer antenatal prophylactic antibiotics. Advise to return for reassessment if there are any further symptoms suggestive of P-PROM or preterm labour.

• Do not use nitrazine to diagnose P-PROM.

• Do not perform diagnostic tests for P-PROM if labour becomes established in a woman reporting symptoms suggestive of P-PROM.

Identifying infection in women with P-PROM

Use clinical assessment and tests (C-reactive protein, white blood cell count and fetal heart rate using cardiotocography) to diagnose intrauterine infection in women with P-PROM. Do not use any one of these in isolation to confirm or exclude intrauterine infection in women with P-PROM.

If clinical assessment or any of the tests are inconsistent, continue to observe the woman and consider repeating the tests.

Premature labour treatment and management¹

Once a diagnosis of premature labour has been made, the priority should be to ensure that the pregnant mother is transported to the safest available facility for delivery of a preterm infant:

• If the patient is at home and the labour appears well established, or if the fetus is visualised on examination, a midwife and an ambulance should be summoned.

• If the patient is in hospital, the emergency paediatric team should be alerted.

A Cochrane review of prophylactic antibiotics for inhibiting preterm labour with intact membranes did not demonstrate any benefit in important neonatal outcomes with the use of prophylactic antibiotics for women in preterm labour with intact membranes, although maternal infection may be reduced. Of concern was the finding of short-term and longer-term harm for children of mothers exposed to antibiotics.³

Tocolytic drugs

• Consider nifedipine for tocolysis if between 24+0 and 25+6 weeks with intact membranes and suspected preterm labour.

• Offer nifedipine for tocolysis if between 26+0 and 33+6 weeks with intact membranes and suspected or diagnosed preterm labour.

• If nifedipine is contra-indicated, offer oxytocin receptor antagonists for tocolysis.

• Do not offer betamimetics for tocolysis.

Corticosteroids

NICE recommends:

• If between 22+0 and 23+6 weeks and suspected or established preterm labour, and planned preterm birth or P-PROM, discuss the use of maternal corticosteroids in the context of individual circumstances.

• Offer maternal corticosteroids if between 24+0 and 33+6 weeks with suspected, diagnosed or established preterm labour, and planned preterm birth or have P-PROM.

• Consider maternal corticosteroids if between 34+0 and 35+6 weeks with suspected, diagnosed or established preterm labour, and planned preterm birth or have P-PROM.

• Consider a single repeat course of maternal corticosteroids for women less than 34+0 weeks of pregnancy who:

  • Have already had a course of corticosteroids when this was more than seven days ago; and

  • At very high risk of giving birth in the following 48 hours.

• If less than 30+0 weeks or if suspected growth restriction, take into account the possible impact on fetal growth of a repeat course of maternal corticosteroids.

• Do not give more than two courses of maternal corticosteroids for preterm birth.

Magnesium sulfate for neuroprotection

Magnesium sulfate has been shown not to be an effective tocolytic; however, it does reduce the risk of cerebral palsy.

• The NICE guideline does not recommend using magnesium sulfate beyond 24 hours. But if uncertainty around exact timing of delivery results in repeat administration, follow the MHRA safety advice on the prolonged or repeated use of magnesium sulfate in pregnancy.

• If between 23+0 and 23+6 weeks and established preterm labour or planned preterm birth within 24 hours, discuss intravenous magnesium sulfate for neuroprotection of the baby. Offer intravenous magnesium sulfate for neuroprotection of the baby if between 24+0 and 29+6 weeks of pregnancy, and established preterm labour, or having a planned preterm birth within 24 hours.

• Consider intravenous magnesium sulfate for neuroprotection of the baby if between 30+0 and 33+6 weeks, and in established preterm labour, or having a planned preterm birth within 24 hours.

• Give a 4 g intravenous bolus of magnesium sulfate over 15 minutes, followed by an intravenous infusion of 1 g per hour until the birth or for 24 hours (whichever is sooner). Monitor for clinical signs of magnesium toxicity at least every four hours by recording pulse, blood pressure, respiratory rate and deep tendon (eg, patellar) reflexes.

• If a woman has or develops oliguria or other evidence of renal failure, monitor more frequently for magnesium toxicity, and reduce or stop the dose of magnesium sulfate.

Emergency cervical cerclage¹

• Aims to delay the birth, and so increase the likelihood of the baby surviving and of reducing serious neonatal morbidity.

• Do not offer emergency cervical cerclage to women with signs of infection, active vaginal bleeding, or uterine contractions.

• Consider emergency cervical cerclage for women between 16+0 and 27+6 weeks with a dilated cervix and exposed, unruptured fetal membranes. Also take into account gestational age (benefits likely to be greater for earlier gestations) and extent of cervical dilatation. Discuss with a consultant obstetrician and consultant paediatrician.

Labour and delivery

If the presentation of the baby is cephalic then most preterm babies will be safely delivered vaginally with only a few requiring delivery by caesarean section.⁴

For women in suspected, diagnosed or established preterm labour, there are no known benefits or harms for the baby from caesarean birth, but the evidence is very limited.

Consider caesarean birth for women presenting in suspected, diagnosed or established preterm labour between 26+0 and 36+6 weeks of pregnancy with breech presentation.

Fetal heart rate monitoring will be required during labour, with either external ultrasound or intermittent auscultation. Neither fetal scalp electrodes nor fetal blood sampling are usually recommended below 34⁺⁰ weeks of gestation.

Timing of cord clamping for preterm babies (born vaginally or by caesarean birth):

• Wait at least 60 seconds before clamping the cord of preterm babies unless there are specific maternal or fetal conditions that need earlier clamping.

• Position the baby at or below the level of the placenta before clamping the cord.

Prognosis¹

• Babies born preterm have high rates of neonatal and infant mortality, and the risk of mortality increases as gestational age at birth decreases.

• Babies who survive preterm birth have increased rates of disability. Recent UK studies comparing cohorts born in 1995 and 2006 have shown improved rates of survival (from 40% to 53%) for extreme preterm births (born between 22 and 26 weeks). Rates of disability in survivors were largely unchanged over this time period.

• The major long-term consequence of prematurity is neurodevelopmental disability. Although the risk for the individual child is greatest for those born at the earliest gestational ages, the global burden of neurodevelopmental disabilities depends on the number of babies born at each of these gestations, and so is greatest for babies born between 32 and 36 weeks, less for those born between 28 and 31 weeks, and least for those born at less than 28 weeks of gestation.

Premature labour prevention¹

Both intravaginal progesterone and cervical cerclage are used prophylactically to prevent P-PROM in different circumstances. See the separate Preterm Prelabour Rupture of Membranes article for more details. NICE recommends:

Care of women at risk of preterm labour

• Offer prophylactic vaginal progesterone or prophylactic cervical cerclage to women who have both:

  • A history of spontaneous preterm birth (up to 34+0 weeks of pregnancy) or loss (from 16+0 weeks of pregnancy onwards), and

  • Transvaginal ultrasound scan carried out between 16+0 and 24+0 weeks of pregnancy shows a cervical length of 25 mm or less.

• Consider prophylactic vaginal progesterone for women who have either of these criteria but not both.

• When using vaginal progesterone, start treatment between 16+0 and 24+0 weeks of pregnancy and continue until at least 34 weeks.

• Consider prophylactic cervical cerclage if a transvaginal ultrasound scan carried out between 16+0 and 24+0 weeks of pregnancy shows a cervical length of 25 mm or less, and either a history of preterm prelabour rupture of membranes (P-PROM) in a previous pregnancy or a history of cervical trauma.

Antenatal prophylactic antibiotics for women with P-PROM

• As prophylaxis for intrauterine infection, offer women with P-PROM oral erythromycin 250 mg 4 times a day for a maximum of 10 days or until the woman is in established labour (whichever is sooner).

• For women with P-PROM who cannot tolerate erythromycin or in whom erythromycin is contraindicated, consider an oral penicillin for a maximum of 10 days or until the woman is in established labour (whichever is sooner).

• Do not offer women with P-PROM co-amoxiclav as prophylaxis for intrauterine infection.