A QUARTER of miscarriages may be preventable, research suggests.

Being underweight or obese before conception, working nights, drinking alcohol in pregnancy and lifting heavy loads could all increase the risk, experts said.

They said if women cut these risks to very low levels, 25% of miscarriages could be prevented.

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The large study of more than 91,000 pregnancies also confirmed that one of the biggest factors influencing miscarriage is the mother's age, with women over 30 having a higher chance of miscarrying.

However, other researchers warned the study did not show miscarriage was "caused" by any of the factors and pointed to other limitations.

Professor Tom Bourne, a consultant gynaecologist at Queen Charlotte's and Chelsea Hospital in London, said: "Saying that by changing x or y a percentage of miscarriages could be prevented is quite a statement in the absence of an interventional trial."

Patrick Wolfe, professor of statistics at University College London (UCL), added: "It's best to think of this study as identifying potential candidate risk factors that may be associated with miscarriages that occur later in pregnancy, rather than the last word on the subject overall."

The team behind the study, from the University of Copenhagen in Denmark, used data from 91,427 Danish pregnancies between 1996 and 2002. They regarded miscarriage as before 22 weeks of pregnancy and found that 3177 of the total sample of pregnancies resulted in miscarriage.