Steroid injections given to mothers at risk of giving birth prematurely are likely to deliver babies with lower body weights, says a new study.

The study showed that pre-term babies whose mothers received antenatal corticosteroid therapy (ACT) on average weighed 220 grams less than infants who had not received treatment. The weight difference was 141 grams for near term babies and 89 grams for full-term babies.

In addition, babies who received ACT but delivered at term were also smaller in size when matched against babies born at term without the treatment. "We have known from animal studies that steroid treatment could affect foetal growth. It is still unclear whether the reduction in birth weight of the treated infants is directly caused by the drug or due to the complications that led to the treatment," said Professor Alina Rodriguez from the University of Lincoln. "This study adds weight to calls for a review of the current guidelines for management of threatened pre-term birth and for who should receive steroid treatment," Rodriguez added.

For the study, the team used data from 2,78,508 births to see if the link between reduced birth weight and size was related to the steroid treatment or to other factors. The findings, published in the journal PLOS Medicine, showed that more than four per cent of children were born pre-term (before 37 weeks).

A total of 4,887 women were given ACT, and 2,173 exposed babies were born at term (37 weeks). The fact that this treatment may reduce the foetal growth should be considered in future research and recommendations, suggested Marjo-Riitta Jarvelin, Professor from the varsity.

Worldwide, about 1.5 million babies are born premature annually. Complications resulting from premature birth, especially those related to breathing problems, are the leading cause of death in infants and morbidity in survivors. Therefore, ACT is used before birth to help mature the lungs rapidly.