A one-time set of steroid injections for pregnant women at high risk of giving birth prematurely can head off major problems for the baby, but more injections give no further benefit, Canadian researchers said.

From previous studies, it was known that giving these women a single course of injections of corticosteroids reduces the risk of the baby dying, having bleeding in the brain or having breathing problems due to underdeveloped lungs. The steroids speed the development of the fetal lungs and blood vessels.

But a study of 1,858 women in 20 countries, published in the Lancet medical journal, showed that additional injections every 14 days did not improve the health of the babies and actually resulted in smaller babies.

All the women received an initial course of injections. After that, about half got additional injections every two weeks up to the 33rd week of pregnancy, or delivery, if that occurred first. The others got placebos at the same intervals.

"The key findings from our study were that there was no benefit (from the repeated courses of injections) and therefore that repeated doses should not be used," Dr Kellie Murphy of the University of Toronto and Mount Sinai Hospital in Toronto, who led the study, said.

Compared to full-term babies, premature infants have a higher risk of health problems and lasting disabilities including such as lung and gastrointestinal problems, mental retardation, cerebral palsy, vision and hearing loss. They also are more likely to die soon after birth.

Some doctors have been giving women who are at high risk of having a pre-term baby more than one course of the prenatal steroid injections with the belief this could help the developing baby, but the value had been unclear.

Many factors put women at higher risk of premature birth, including chronic conditions like diabetes and high blood pressure, obesity, problems with the uterus, cervix or placenta, smoking, drinking and doing drugs during pregnancy, or being pregnant with twins or other multiples.

Thousands of women globally get these injections.

John Newnham of the University of Western Australia and Karen Simmer of King Edward and Princess Margaret Hospitals in Australia said in a commentary that the evidence suggests it is prudent for obstetricians not to prescribe repeat injections of steroids.

"Single-course therapy is of considerable benefit, but we should be aware of the potential dangers of giving too much of a good thing," they wrote.

Reuters Health