Synonym: preterm 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.
- Around 52,000 babies were born prematurely in England and Wales in 2012; there has been no change in this figure over a 10-year period.The UK has one of the highest rates of premature births in Europe.
- Very premature births occur at less than 32 weeks of gestation. They account for 1.4% of UK births but cause around 51% of infant deaths.
- About 30% of preterm births are unexplained and spontaneous.
- Multiple pregnancy accounts for about another 30% of cases.
- Other known risk factors include:
- Genital tract infection, including bacterial vaginosis.
- Preterm prelabour rupture of membranes (P-PROM).
- Antepartum haemorrhage.
- Cervical incompetence.
- Congenital uterine abnormalities.
- Antiphospholipid syndrome.
- Diabetes mellitus.
- The two strongest risk factors for idiopathic preterm labour are low socio-economic status and previous preterm delivery.
- Worldwide, the greatest risk factor is infection, mainly from malaria, HIV and mycoplasma.
- Around 25% of preterm deliveries are elective due to either maternal factors such as pre-eclampsia or fetal factors such as extreme growth restriction.
Pregnant women may present with a history of painful contractions and assume that they are in a premature labour. Many of these women are experiencing Braxton Hicks contractions and over 60% will not have delivered within 48 hours of presentation, many going on to full term.
Additional indications of preterm labour may be gained through history and examination.
- 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.
- 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 who are <29+6 weeks of gestation in suspected preterm labour do not require further investigations to confirm this.
For women with intact membranes who are >30+0 weeks of gestation:
- Transvaginal ultrasound measurement of cervical length is used to estimate likelihood of delivery within the following 48 hours:
- If the cervix is >15 mm it is unlikely she is in preterm labour.
- Fetal fibronectin is a quick, simple test that may be used as an alternative when transvaginal ultrasound measurement of cervical length is unavailable or unacceptable:
- It requires that an internal examination has not been undertaken first.
- If fibronectin concentration is ≤50 ng/ml it is unlikely she is in preterm labour.
- Vaginal swab - this should be taken in all women with possible premature labour who are being examined, as this will allow appropriate antibiotic therapy to be given if an infection develops at a later stage.
- The use of nitrazine sticks is no longer recommended.
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.
- Tocolysis may be considered for women with suspected preterm labour who have had an otherwise uncomplicated pregnancy.
- Women most likely to benefit from use of a tocolytic drug are those who are in very preterm labour, those needing transfer to a hospital which can provide neonatal intensive care and those who have not yet completed a full course of corticosteroids.
- Tocolytics should not be used in women with P-PROM.
- If the decision is made to use a tocolytic drug, nifedipine is the drug of first choice (unlicensed use); if nifedipine is contra-indicated, offer an oxytocin receptor antagonist (atosiban):
- Nifedipine and atosiban seem to have comparable effectiveness in delaying delivery for up to seven days, with fewer maternal adverse effects and less risk of rare serious adverse events than alternatives such as ritodrine or indometacin.
- A systematic review and network meta-analysis on trials of tocolytics found that prostaglandin inhibitors and calcium-channel blockers seem to be the best treatment for preterm delivery, on the basis of the four outcomes:
- Delivery delayed by 48 hours.
- Neonatal mortality.
- Neonatal respiratory distress syndrome.
- Maternal side-effects.
- Using multiple tocolytic drugs appears to be associated with a higher risk of adverse effects and so should be avoided.
- Women receiving tocolytics should be informed that, whilst it is hoped that these drugs will prolong their pregnancy, such drugs may not make their babies healthier.
- Maternal corticosteroids should be considered if the mother is between 24+0 and 35+6 weeks of gestation.
- Antenatal corticosteroids are associated with a significant reduction in neonatal deaths, respiratory distress syndrome and intraventricular haemorrhage.
- Benefits are seen even when delivery occurs within 24 hours of the first dose.
- Data confirming benefits are greatest for gestations between 26+0 and 34+6 weeks.
- They have no benefits for the mother but are safe for her to take.
- Various dosing schedules are used. They all provide 24 mg of either betamethasone or dexamethasone intramuscularly over a 24- to 48-hour period.
Magnesium sulfate for neuroprotection
Magnesium sulfate has been shown not to be an effective tocolytic; however, it does reduce the risk of cerebral palsy.
- Women who are between 24+0 and 29+6 weeks of gestation and who are expected to deliver within the following 24 hours should be offered magnesium sulfate for up to 24 hours.
- It may also be considered in women between 30+0 and 33+6 weeks of gestation.
- 4 g is given as a single intravenous bolus followed by an infusion of 1 g/hour over 24 hours or until delivery, whichever is sooner.
- Monitoring is required for signs of maternal magnesium toxicity.
Emergency cervical cerclage
- Consider emergency or 'rescue' cervical cerclage to women between 16+0 and 34+0 weeks who have a dilated cervix and exposed unruptured fetal membranes.
- It should not be considered for women with:
- Any signs of infection.
- Any bleeding.
- Uterine contractions.
- 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.
- Breech presentations below 32 weeks of gestation will usually be more safely delivered by caesarean section.
- Fetal heart rate monitoring will be required during labour, with either external ultrasound or intermittent auscultation:
- Use of fetal scalp electrodes is not usually recommended below 34+0 weeks of gestation.
- Fetal blood sampling is not recommended below 34+0 weeks of gestation
- Babies delivered with optimal care after 30 weeks most often survive without any lasting abnormality.
- Survival and impairment in early childhood are both closely related to gestational age for babies born at less than 27 weeks of gestation.
- A higher proportion of babies admitted for neonatal care now survive without disability, particularly those born at gestational ages 24 and 25 weeks.
- Although survival of babies born between 22 and 25 weeks of gestation has increased over a period of two decades, the pattern of major neonatal morbidity and the proportion of survivors affected are actually unchanged.
- Preterm birth can have huge psychosocial and emotional effects on the family, as well as being costly for health services.
- Both intravaginal progesterone and cervical cerclage are used prophylactically to prevent P-PROM in different circumstances. See separate Preterm Prelabour Rupture of Membranes article for more details.
- Despite bacterial vaginosis being confirmed as a risk factor for preterm birth and miscarriage, the routine use of antibiotics in women with subclinical infection in preterm labour with intact membranes is controversial. There is evidence that antibiotics given in these circumstances are associated with an increased risk of functional impairment and cerebral palsy in children at age 7.
Further reading and references
Perinatal Management of Pregnant Women at the Threshold of Infant Viability (The Obstetric Perspective), Scientific Impact Paper No. 41; Royal College of Obstetricians and Gynaecologists, Feb 2014
Born Too Soon - The Global Action Report on Preterm Birth; World Health Organization, 2012
Preterm labour and birth; NICE Quality Standard, October 2016
Preterm labour and birth; NICE Guidelines (November 2015)
Beck S, Wojdyla D, Say L, et al; The worldwide incidence of preterm birth: a systematic review of maternal mortality and morbidity. Bull World Health Organ. 2010 Jan88(1):31-8. doi: 10.2471/BLT.08.062554. Epub 2009 Sep 25.
Preterm Labour, Tocolytic Drugs (Green-top Guideline No. 1B); Royal College of Obstetricians and Gynaecologists (February 2011)
Haas DM, Caldwell DM, Kirkpatrick P, et al; Tocolytic therapy for preterm delivery: systematic review and network meta-analysis. BMJ. 2012 Oct 9345:e6226. doi: 10.1136/bmj.e6226.
Alfirevic Z; Tocolytics: do they actually work? BMJ. 2012 Oct 9345:e6531. doi: 10.1136/bmj.e6531.
Antenatal Corticosteroids to Reduce Neonatal Morbidity and Mortality; Royal College of Obstetricians and Gynaecologists (October 2010)
Reddy UM, Zhang J, Sun L, et al; Neonatal mortality by attempted route of delivery in early preterm birth. Am J Obstet Gynecol. 2012 Aug207(2):117.e1-8. doi: 10.1016/j.ajog.2012.06.023. Epub 2012 Jun 19.
Moore T, Hennessy EM, Myles J, et al; Neurological and developmental outcome in extremely preterm children born in England in 1995 and 2006: the EPICure studies. BMJ. 2012 Dec 4345:e7961. doi: 10.1136/bmj.e7961.
Costeloe KL, Hennessy EM, Haider S, et al; Short term outcomes after extreme preterm birth in England: comparison of two birth cohorts in 1995 and 2006 (the EPICure studies). BMJ. 2012 Dec 4345:e7976. doi: 10.1136/bmj.e7976.
Preterm Labour, Antibiotics, and Cerebral Palsy; Royal College of Obstetricians and Gynaecologists Scientific Impact Paper No 33 February 2013