A major study has found that their babies are up to 60 per cent more likely to develop the disease during childhood.
Academics say the Government should issue warnings to pregnant women to limit their coffee intake just as they are told to cut back on alcohol and stop smoking.
They think caffeine may change the DNA in the foetus’s cells making them more susceptible to the development of tumours.
Researchers who looked at more than 20 existing studies found that babies of women who drank coffee during pregnancy were 20 per cent more at risk of developing leukaemia. But if they drank more than two cups a day the risk rose to 60 per cent.
And for women who had four or more cups a day it rose to 72 per cent, according to the study published in the American Journal of Obstetrics and Gynaecology.
Around 500 children are diagnosed with leukaemia in the UK every year and it is by far the most common childhood cancer.
Fortunately, if detected early enough it can be treated with chemotherapy and survival rates are around 80 per cent.
But despite decades of research, scientists have been unable to pinpoint its cause and previous links to power lines and nuclear power plants have been dismissed.
The study concludes: ‘The findings suggest that maternal coffee consumption during pregnancy may increase the risk of childhood leukaemia.
Because of limited studies, further prospective studies are urgently needed to explore the adverse effect of coffee consumption on childhood leukaemia.’
Denis Henshaw, Emeritus Professor of Human Radiation Effects at Bristol University, who was not involved in the research but is an expert in the field said: ‘I don’t think women should give up coffee altogether during pregnancy but as a precaution they should limit their intake.
‘This could be to less than two cups a day or maybe even as far as only having it occasionally.
‘The findings are very striking that the risk is 60 per cent higher for just two cups a day.
He added: ‘The incidence of childhood leukaemia has increased steadily in recent decades.
‘So if things are changing over a short-term scale we have to suspect some environmental factor and there can be more than one of them.
‘There are lots of things out there we don’t like, power lines, magnetic fields, pollution, all sorts of things.
‘Coffee drinking has become popular, with well-known coffee shops expanding, so coffee drinking has become very popular in the UK.
The NHS advises pregnant women to limit themselves to 200mg of caffeine a day, equivalent to one and a half cups of filter coffee or two of instant.
But the advice is relaxed and it tells women not to worry if they exceed this amount as the ‘risks are small.’
Tory MP Andrew Percy, who sits on the Commons Health Select Committee said: ‘This is an interesting study that requires further investigation.
‘If there are robust findings which show an association between drinking coffee during pregnancy and leukaemia, then it makes sense that guidance be issued to women so they can make an informed choice about whether to drink coffee when expecting.