In turn, mothers are less likely to want to return to work after giving birth because of the treatment they receive during pregnancy.
Researchers told the Women's Psychology Conference at Birmingham University yesterday that pregnant women felt they were undervalued as workers and not seen as effective by employers and colleagues. This is despite the fact that the majority of pregnant women continue to work, with more than three-quarters working up to the third trimester.
The researchers questioned 200 men and women from a variety of backgrounds - including manufacturing industry and academic. Around 50 per cent of those interviewed saw pregnancy and work as a bad combination.
However, there was a strong gender divide with up to 70 per cent of men seeing pregnant workers in a negative light compared with one-third of women.
"Women were treated as if they were already mothers of young children, with all the issues of whether it's wrong for women to go out to work," said Dr Helen Pattison of Birmingham University, which carried out the research.
"Pregnancy was also seen as a time of debilitation, when women were physically incapacitated and also became emotional with wide mood swings and forgetfulness," she said.
One man in the survey commented: "Women who become pregnant should suffer the consequences if they lose money from their jobs."
Others thought that many jobs became too dangerous for women in pregnancy. One man also said that for women in their first pregnancy their work would be affected because of their "uncertainty" and "lack of confidence", whereas older pregnant women should not work because of the "danger" to the child.
Dr Pattison said: "There is this notion of the home as a place of safety and work as a place of danger for mothers. Yet we know from other work that the home is an area of more danger."
Those with more positive views said that employers should take responsibility for their staff. One man said: "Pregnancy is a normal and vital part of living in society and employers should support both parents."
The researchers said that their study helped understanding of prejudice against working while pregnant, which could help in planning future social policy.
"It's a bit depressing," said Dr Harriet Gross, co-author of the study. "It is difficult enough for women in the workplace with children, never mind pregnant women. It is not going to encourage women back into the workplace unless maternity is viewed in a more positive experience."
Another study from Dundee University found that men thought that women had achieved gender equality, whereas women still thought there was a long way to go.
The study looked at how men and women believed that gender roles and stereotypes had changed between 1945 and 1997 and how they were likely to change again by 2040.
It found that both sexes believed there were significant changes in women's behaviour from past to present, with their involvement in traditional "masculine" roles - career, education and leisure activities - increasing and childcare and home responsibilities decreasing.
Women also believed that they worked harder than men and they thought they were more assertive, stronger and more intelligent than the male group.