Introduction

Preterm birth is the major cause of neonatal and infant mortality in the developed world, being responsible for 55% and 43% of neonatal and infant deaths, respectively, in England and Wales.1 With nearly 50 000 preterm births (before 37 weeks gestation) a year in England and Wales (7.6%), the burden is large and research has estimated the annual cost of these babies to be nearly £3 billion2 reflecting both initial care costs and ongoing morbidity.

To date, both the clinical response and the research agenda have concentrated on two main areas: (1) optimising neonatal care practices and interventions and (2) secondary preventive strategies after preterm birth is threatened or an underlying condition recognised. In terms of neonatal care, there have been major advances in the past 30 years particularly in infants of 32 weeks gestation or less; however, it is unlikely that further dramatic changes will be seen particularly among those babies born at the borders of viability. In the same period, obstetric research has focused on strategies to prevent preterm birth once it is threatened but although progesterone therapy is currently showing some promise,3 other obstetric measures have shown little benefit.4