Tocolysis: current controversies, future directions

The use of tocolytic agents for the treatment of preterm labor is not supported by the current evidence from placebo-controlled trials. Despite this, tocolytics continue to be widely used in clinical practice. Possible reasons for the lack of observed benefit include the hypothesis that suppression of labor may be harmful in some situations, along with a failure to appreciate the implications of the complex physiology of parturition. Importantly, however, it must be recognized that the quality of evidence addressing the question is poor, with studies significantly underpowered to detect changes in health outcomes. Where tocolysis is used, recent trends have favored agents with lower maternal side effect profiles, including calcium channel blockers and the oxytocin receptor antagonist atosiban. The use of cyclooxygenase-selective inhibitors of prostaglandin synthesis is currently being explored. Future directions in tocolytic research include the use of multiple agent therapies, along with the development of more selective treatments with low side effect profiles. Such agents include oxytocin receptor antagonists with more favorable pharmacological properties and prostaglandin F2alpha receptor antagonists. Future research into tocolytic therapies must focus on evaluating health outcomes from treatments rather than simply the ability to prolong pregnancy, and consequently the design of appropriate clinical studies needs careful consideration with respect to issues such as inclusion criteria, sample size and the selection of appropriate outcome measures.