Pregnant women have been urged to limit their daily consumption of caffeine to 200mg, the equivalent of two mugs of coffee.
The Foods Standard Agency has issued the guidance after studies linking it with lower birth weight and health conditions later in life.
Its previous guidance suggested a maximum daily caffeine intake of 300mg, but this was revised this following research carried out by the universities of Leeds and Leicester.
Andrew Wadge, Chief Scientist at the FSA, said: 'This new advice doesn’t mean that pregnant women have to cut out caffeine completely, simply that they should be careful and make sure they don't have too much.
‘We would emphasise that the risks are likely to be very small and believe our new advice, which is based on new research and has been considered by leading independent scientists, is sensible and proportionate.'