Introduction

In most jurisdictions an infant is regarded as premature when delivered at fewer than 37 weeks gestation [1,2]. The proportion of babies born prematurely rather than at term is small: 18% in the United States in 2009 [3], 12% in England and Wales [4], and 7.4% in Australia [5]. But the risks to a pre-term infant are significant and those risks increase with greater prematurity. In England, Wales, and Northern Ireland, there is nearly one neonatal death per 1000 live births at term, but this rises to 204 deaths per 1000 births in babies born between 24 and 27 weeks gestation [6]. Further, especially in this latter very pre-term group, survivors display significant morbidity, including chronic respiratory disease, ultrasound-detected brain injury, and retinopathy of prematurity [7]. While there is evidence of a reducing mortality in most pre-term gestations, there are some indications that this is at the expense of increased morbidity [8]. Even late pre-term babies have a higher risk of morbidity, particularly respiratory problems and infectious diseases, than term infants [9].

Premature birth is spontaneous and without a specific recognized cause in some 31–51% of cases, but there is an increased risk associated with multiple pregnancy (12–28%), premature membrane rupture (6–40%), cervical incompetence (8–9%), and antepartum hemorrhage (6–9%). Associated ascending infection may be a significant factor in some of these conditions [10]. An obstetric decision to deliver early may be influenced by a number of additional factors, such as fetal growth restriction and maternal hypertension.