ONLY 40 per cent of mothers believe their bosses know how to manage pregnant staff, according to a new report today.

Many complain they have been badly treated on returning to work after maternity leave.

A survey of more than 2,000 mothers also found that only half were fully aware of their rights at work while pregnant or returning to their job.

One in six polled by the Equal Opportunities Commission said they were not treated well by their employer when they were pregnant.

One in four complained of poor treatment when they went back to work after having a baby.

A two-year investigation by the EOC found that smaller firms faced particular problems because managers often had little experience of dealing with pregnant staff.

EOC chairwoman Jenny Watson said: "Women are now nearly half the workforce. There's no turning back from this major social change, so it's vital that workplaces are equipped to make pregnancy at work a good experience.

"If we fail to tackle the knowledge gap surrounding the rights of pregnant women and new parents at work, we run the risk of seeing these women drop out of the workforce altogether.

"Those who have been unfairly treated while pregnant suffer financially and emotionally and are far less likely to return to their jobs.

"As well as damaging families, this costs employers millions in recruitment and training and causes significant damage to Britain's economic productivity."

Dorset Business chief executive, Peter Scott, said: "Being a supportive and caring employer isn't always easy, and you cannot expect to turn your back on changing work/family patterns.

"Watch for the biological clock ticking, and don't be surprised when your female staff start or add to their family."

Federation of Small Businesses spokesman Stephen Alambritis said: "The more support small businesses are given, the greater the chance that they will understand their rights and obligations.

"This is all the more important, given the EOC investigation's finding that smaller businesses encounter, on average, one pregnancy per 10 years."