Drugs used for the past 20 years to arrest premature labour do nothing to help improve birth weight or perinatal mortality, a Canadian study group has discovered.

It had been assumed that the drugs beta adrenergic agonists reduced perinatal mortality and the frequency of long term handicaps by reducing the rate of prematurity.

The study group, the Canadian Preterm Labor Investigators Group, decided to assess the risks and benefits of the drugs to the mother and infant before and after delivery. They randomly selected 708 women with preterm labour at six hospitals to receive an injection of either beta adrenergic agonist ritodrine or a placebo.

Their first objective was to discover the effect of ritodrine on prenatal mortality, while also evaluating the causes of perinatal death, the extent to which delivery was delayed with ritodrine, and the effects on birth weight, maternal deaths, neonatal deaths and infant deaths at 18 months.

They confirmed that the ritodrine would indeed arrest labour by up to 48 hours, but little else. It had "no significant beneficial effect" on mortality, nor on weight or prolongation of the pregnancy to term.

They concluded that it is important to use the time gained more beneficially. Since the use of glucocorticoid hormones during preterm labour had been shown in trials to decrease neonatal mortality, more liberal use of it "might have substantial benefit". In fact, the group has recommended that ritodrine not be used after 28 weeks' term unless used so the mother can receive glucocorticoid treatment as well.