Intended for healthcare professionals

Practice Uncertainties

Which intervention reduces the risk of preterm birth in women with risk factors?

BMJ 2016; 355 doi: (Published 05 October 2016) Cite this as: BMJ 2016;355:i5206
  1. Sarah J Stock, senior clinical lecturer in maternal and fetal medicine1,
  2. Khaled M K Ismail, professor of obstetrics and gynaecology2
  1. 1Tommy’s Centre for Maternal and Fetal Health, MRC Centre for Reproductive Health, University of Edinburgh Queen’s Medical Research Institute, Edinburgh, UK
  2. 2Birmingham Centre for Women’s and Children’s Health, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
  1. Correspondence to: K M K Ismail k.ismail{at}

What you need to know

  • The best intervention for prevention of spontaneous preterm birth in women with risk factors is still unclear

  • In women with a singleton pregnancy risk of preterm birth and with a short cervix, the evidence for use of cervical cerclage is clearer than that for progesterone or cervical pessary

  • Discuss with parents that prevention of preterm delivery might not necessarily translate into improved health in children

The aim of preventing preterm birth is to improve the health of babies by prolonging pregnancy. Preterm birth, or delivery before 37 weeks’ gestation, affects 7.3% of pregnancies in the UK.1 Around 75% of these births result from spontaneous preterm labour. The remaining 25% are delivered for medical reasons and are not considered further in this article.

Who is at risk?

Box 1 lists clinical risk factors and ultrasound scan findings that are associated with an increased risk of spontaneous preterm birth. However, these factors have poor predictive value. Women with multiple pregnancy are also at high risk of preterm birth, and their management is discussed in the supplementary online material.

Box 1: Risk factors for preterm birth234

Clinical history*
  • History of mid-trimester loss

  • Preterm prelabour rupture of membranes in a previous pregnancy

  • Preterm birth in a previous pregnancy

  • History of cervical treatment for cervical intraepithelial neoplasia

  • Short cervix (<25 mm) on transvaginal ultrasound examination

  • *The presence of any of the clinical risk factors listed can be considered a trigger for screening of cervical length by transvaginal ultrasound scan

Appraising the evidence

Three treatment interventions are available to women at risk of spontaneous preterm birth (fig 1). Considerable uncertainty exists over the effectiveness of these interventions, however, in part because clinical trials are hard to perform. Large numbers of trial participants are needed because most women at high risk of spontaneous preterm birth deliver at term, even without treatment. It is difficult and expensive to include neonatal and childhood …

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