Pregnant women at risk of preterm delivery should not be given multiple doses of steroids, say researchers.
The drugs are given to promote lung development in the foetus and increase the chances of survival.
However, a study of 1,800 women, which has been published in the journal The Lancet, suggested multiple courses of steroids do not improve outcomes after premature birth and may lead to smaller babies.
According to Canadian researchers, doctors should stick to one course of treatment, reports BBC.
For the new research, Dr Kellie Murphy, study leader and obstetrician at Mount Sinai Hospital in Toronto, and her colleagues studied 1,858 women at 25 to 32 weeks of gestation who had not delivered their babies within 14 to 21 days after receiving one dose of corticosteroids.
The women were randomly assigned to corticosteroids every 14 days until 33 weeks of gestation or until they delivered, or a placebo. The researchers looked for cases of death before or after delivery and other conditions, such as severe respiratory distress syndrome and bleeding in the brain.
Murphy's team found that women given multiple doses of corticosteroids had babies that weighed less, were shorter and had smaller head circumference than babies of mothers given a placebo.
Also, there was no difference in other results, such as death, respiratory problems and bleeding in the brain between the babies of women given more than one dose of steroids and women given a placebo, the researchers reported.