It brings NICE in line with government advice and replaces previous guidance saying small daily amounts were fine.

However, NICE concedes there is no evidence to support the change.

Not everyone agrees with such a tough approach, but research into the impact of alcohol is patchy.

The Royal College of Obstetricians and Gynaecologists said there was no evidence that a couple of units once or twice a week would do any harm to the baby - but could not categorically rule out any risk.

NICE, which is responsible for the promotion of good health in England, Wales and Northern Ireland, decided to tighten its guidance partly because of concern that people are now drinking more than in the past.

Previous draft guidance suggested pregnant women could drink a unit of alcohol a day.

NICE deputy chief executive Dr Gillian Leng said people, and in particular women, were drinking more and the NHS advisory body wanted to send a "clear message".

"I think it reinforces the advice which came out last year. Women should be advised not to drink."

See table of alcohol units
The Department of Health in England revised its guidance last year, calling for no drinking while pregnant or while trying to get pregnant.

Professor Sir Liam Donaldson, Chief Medical Officer for England, welcomed the new guidance from NICE, stressing that it was particularly important not to drink at the beginning of pregnancy, when the risk of miscarriage was highest.

Drinking heavily in pregnancy can cause foetal alcohol syndrome, which can leave children with features like small heads, widely spaced eyes and behavioural or learning problems.