Introduction

The delivery of infants at preterm periods of gestation is a major factor contributing to perinatal morbidity and mortality in current obstetric practice in developed countries (ACOG Practice Bulletin 2001). It is associated with short- and long-term sequelae and constitutes a significant problem in terms of mortality, disability and cost to healthcare resources and society. Research efforts to address this problem have increased substantially over the last ten years but have failed in their attempts to improve prediction and prevention of preterm delivery.

Preterm delivery results from a series of disorders implicating maternal and fetal disease, some of which are explained and interrelated while many are of unknown aetiology (Iannucci et al. 1996; Burke and Morrison 2000). Epidemiological risk factors for preterm delivery, which are well established (Olsen et al. 1995; Mercer et al. 1996; Kramer et al. 2001), exert a huge influence on its incidence and outcome. In addition, the overall incidence of preterm delivery appears to be increasing in recent years (Goldenberg and Rouse 1998). The reasons for this increase are complex and have been the source of much debate. It has been speculated that there might have been a recent increased tendency to register live birth at very early gestational ages (i.e. 20–22 weeks) in some countries (Joseph et al. 1998).