Scientists have warned that giving repeated courses of steroid drugs to mothers at risk of preterm delivery may be based on unsound evidence.
Babies born before 32 weeks of pregnancy often have neonatal lung disease, a major cause of illness and death.
Several previous analyses concluded that steroids were most effective when given within a week of delivery, which led to repeated treatment for women who did not deliver within this time frame.
However, two researchers have now reported in the British Medical Journal (BMJ) that methodological problems might have rendered conclusions drawn from these analyses wrong.
They also said that the practice of repeating courses was not based on any good evidence, and that it was yet unknown whether the practice was beneficial or harmful.
According to researchers, the analyses of subgroups of people in the research studies were not done correctly, and may have been misleading.
The authors of the report stressed the need for a long-term follow-up to fully understand the benefits and risks of repeated courses of steroids. Until that happens, say the researchers, reanalysis of the data from the original trials may help to clarify whether effectiveness declines with time to delivery, and if so, over what timescale this occurs.
They, however, warn that the new trials should avoid making the same errors in subgroup analyses "or we risk repeating the errors made in the conclusions of the original antenatal steroid trials."