oPatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
Synonym: preterm labour
Infants born as a result of premature labour suffer 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 50,000 babies are born prematurely in the UK each year. 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.
- Preterm rupture of the membranes.
- 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.
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.
- Nitrazine sticks may be useful in detecting the presence of amniotic fluid, signifying rupture of the membranes. However, a false positive result may be given by any substance which has changed the pH of the vagina, such as urine.
- 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.
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.
- If the decision is made to use a tocolytic drug, nifedipine and atosiban seem to have comparable effectiveness in delaying delivery, with fewer maternal adverse effects and less risk of rare serious adverse events than alternatives such as ritodrine or indomethacin.
- Nifedipine (unlicensed use) and atosiban have comparable effectiveness in delaying birth for up to seven days.
- 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 and maternal side-effects.
- Using multiple tocolytic drugs appears to be associated with a higher risk of adverse effects and so should be avoided.
- It has been suggested that women receiving tocolytics should be informed that it is hoped that these drugs will prolong their pregnancy, but that these drugs may not make their babies healthier.
- The exception may be magnesium sulphate, and although it has not been found to be an effective tocolytic, it does reduce the risk of cerebral palsy. Women at risk of premarture delivery should receive magnesium sulphate for 24 hours.
- 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.
- 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.
- The insertion of a cervical suture (cervical cerclage) in early pregnancy has been shown to reduce preterm delivery in women identified as being at high risk (ie women with three or more second-trimester miscarriages or preterm deliveries).
- The detection and treatment of asymptomatic infections such as bacterial vaginosis and asymptomatic bacteriuria have been shown to be effective in preventing premature labour.
Further reading & 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
- 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 Jan;88(1):31-8. doi: 10.2471/BLT.08.062554. Epub 2009 Sep 25.
- Tocolysis for Women in Preterm Labour, 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 9;345:e6226. doi: 10.1136/bmj.e6226.
- Alfirevic Z; Tocolytics: do they actually work? BMJ. 2012 Oct 9;345:e6531. doi: 10.1136/bmj.e6531.
- Reddy UM, Zhang J, Sun L, et al; Neonatal mortality by attempted route of delivery in early preterm birth. Am J Obstet Gynecol. 2012 Aug;207(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 4;345: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 4;345:e7976. doi: 10.1136/bmj.e7976.
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Dr Laurence Knott
Dr Louise Newson
Dr John Cox