Researchers in this week's BMJ question whether giving repeated courses of steroid drugs to mothers at risk of preterm delivery is based on sound evidence.
Babies born before 32 weeks of pregnancy often have neonatal lung disease, a major cause of illness and death - the earlier the birth, the greater the risk.
In the 1990s, the benefit of giving antenatal corticosteroids to prevent lung disease in preterm babies was established. Several analyses concluded that steroids were most effective when given within a week of delivery and this led to repeated treatment for women who did not deliver within this time frame. Many mothers received multiple courses of corticosteroids during the 1990s and early 2000s.
But now two researchers warn that methodological problems in these analyses mean that this conclusion may be wrong and the practice of repeating courses was not based on any good evidence. We do not yet know whether this practice was beneficial or harmful.
The main problem, they say, is that the analyses of subgroups of people in the research studies were not done correctly and may have been misleading.
Several trials are now underway to determine the efficacy and safety of repeated courses of steroids. Results so far have shown no conclusive evidence of short-term benefit but long-term follow-up is needed to fully understand the benefits and risks, say the authors.
Until then, they suggest that 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.
But they warn that these 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."