Researchers at the University of Copenhagen also found that the damage can not be reversed with vitamin C supplements after birth. 

They carried out the tests on guinea pigs because, like humans, they are unable to produce their own vitamin C.

Population studies show that 10-20% of all adults in the developed world suffer from vitamin C deficiency but if pregnant women eat a varied diet and do not smoke, there is no reason to worry. 

The researchers are now trying to figure out how early in pregnancy the neural effects occur.