A mother's poor diet just before conception could be a cause of premature birth, according to researchers who studied undernourished sheep.

Premature births are a problem worldwide, and have been on the rise in Western societies over the past decade. It remains the most common cause of death in newborns, and premature babies are more likely to develop heart, lung and brain disorders. As many as 40 per cent of premature births are unexplained. Poor maternal nutrition could fill in some of those gaps, according to Dr. John Challis, a professor of physiology at the University of Toronto and one of the senior authors of the paper.

Sheep are commonly used to study pregnancy and fetal development. Human studies have also suggested underfed women tend to deliver earlier.

Undernourished ewes are likely to give birth prematurely

Dr. Frank Bloomfield, a pediatrician at the University of Auckland who specializes in treating infants, led the study. The paper appears in Friday's issue of the journal Science.

Bloomfield and his colleagues in Canada and Australia looked at 10 ewes who were moderately undernourished starting 60 days before mating and 30 days afterwards.

The undernourished ewes gave birth an average of 139 days after conception, compared to 146 days for eight ewes who were given all they wanted to eat.

Fetus triggers its birth

The researchers found a premature surge in fetal levels of the hormone cortisol.

A surge in cortisol triggers the chain of events leading to labour in sheep, and it is thought human labour follows the same process.

Bloomsfield said his sheep studies suggest undernourishment in mothers causes the hormone system in the developing fetus to mature early, even though the undernourishment occurred months before birth.

"This supports the concept that maternal nutrition around the time of conception is important for the entire period of gestation," said Dr. Sessions Cole, a premature baby expert at the Washington University in St. Louis, Mo.

The research was funded by the Canadian Institutes of Health Research, the Health Research Council of New Zealand, the Royal Australian College of Physicians and the National Health and Medical Research Council of Australia.