Preterm birth is the most important single determinant of adverse infant outcome, in terms of both survival and quality of life. Although preterm birth is defined as being before 37 completed weeks, most mortality and morbidity is experienced by babies born before 34 weeks. Prevention and treatment of preterm labour is important, not as an end in itself, but as a means of reducing adverse events for the child.
For many women in preterm labour it may not be appropriate to consider attempting tocolysis. Labour may be too advanced, for example, or prolonging the pregnancy may be hazardous because of intrauterine infection or placental abruption. As it is the woman who receives the intervention, there is also a responsibility to ensure that she is not harmed.
A wide variety of agents have been advocated as suppressing uterine contractions. Those in current use include beta-agonists, calcium channel blockers, prostaglandin synthetase inhibitors, nitric oxide donors and oxytocin receptor antagonists. There is little reliable information about current clinical practice but it is likely that ritodrine hydrochloride, a beta-agonist, remains the most widely used. Magnesium sulphate is popular for tocolysis in the USA and some other parts of the world, but is rarely used for this indication in the UK.
Tocolysis has also been advocated for the management of intrapartum fetal distress, impaired fetal growth and to facilitate external cephalic version at term. These uses are not considered in this guideline.
The aim of this guideline is to summarise the evidence about the effectiveness of tocolytic drugs for preterm labour and to provide guidance as to how to incorporate this evidence into clinical practice.