Introduction

The ethos of basing practice on the best available evidence is well established in perinatal medicine. The introduction to clinical practice of major interventions, such as antenatal corticosteroids and exogenous surfactant, was informed by evidence from seminal randomised controlled trials and systematic reviews.

Equally important has been the development and evaluation of interventions that have been shown not to have major benefits for preterm infants. For example, strong evidence from preclinical research studies indicated that antenatal thyrotropin releasing hormone might act synergistically with corticosteroids to reduce the risk of respiratory distress syndrome in preterm infants. Despite the biological plausibility of this treatment and evidence of effect in animal models, randomised controlled trials (involving over 4500 women) did not show any improvement in outcomes, including mortality, for preterm infants. Also, antenatal thyrotropin releasing hormone was shown to be associated with adverse effects for mothers and infants, including a higher risk of infants needing mechanical ventilation. On the basis of this evidence, antenatal thyrotropin releasing hormone does not have a role in the management of threatened preterm birth.

Evidence

Obtaining the best evidence to guide clinical practice is not always easy. In particular, undertaking clinical trials to evaluate interventions for preterm infants is difficult. Although about 3000 randomised controlled trials have been reported in the field of neonatology, many interventions have not yet been subjected to unbiased evaluation. This could be because the trials have not been attempted, or have been flawed methodologically, or have been too small to detect clinically important effects. Large perinatal trials have problems with recruitment. This could be related to the issues surrounding the public perception of perinatal trials and the …