Preterm labour is still the main cause of perinatal morbidity and mortality in the developed world. Despite a better understanding of the pathophysiology, and the recognition that it is a syndrome with multiple causes, rates continue to rise.1 In the linked cohort study (doi:10.1136/bmj.b744), de Heus and colleagues assess the incidence of serious maternal complications with the use of tocolytic drugs for the treatment of preterm labour.2

Corticosteroids given to women at risk of preterm birth increase fetal lung maturity and can reduce fetal death, intraventricular haemorrhage, and respiratory distress by up to 50%.3 In contrast, it is still unclear whether tocolysis improves neonatal or longer term outcomes.4 Thus, the Royal College of Obstetricians and Gynaecologists’ clinical guideline on tocolysis concludes that, “it is reasonable not to use tocolytic drugs.”5

Despite the lack of evidence, several tocolytic drugs are commonly used worldwide. They are used primarily to delay delivery for up to 48 hours to allow for administration of corticosteroids or transfer to a unit with neonatal intensive care facilities (or both). Little consensus exists as to which tocolytic agent …