Women who are pregnant or trying for a baby should stop drinking alcohol altogether, the Government's leading doctors give warning today.

The new advice radically revises existing guidelines, which say that women can drink up to two units once or twice a week. Fiona Adshead, the deputy chief medical officer, said that the change was meant to send "a strong signal" to the thousands of women who drank more than the recommended limit that they were putting their babies at risk. But she admitted that it was not in response to any new medical evidence.

Women are often confused about what drinking in moderation really means, the new guidelines say, and surveys suggest that many accidently or deliberately exceed the limit. "Our advice is simple: avoid alcohol if pregnant or trying to conceive," Dr Adshead said. "We have strengthened our advice to women to help ensure that no one underestimates the risk to the foetus."

She suggested that bottles of beer, wines and spirits should carry the new warning that pregnant women give up drinking. However, it emerged yesterday that the Royal College of Obstetricians and Gynaecologists intended to stick with its advice that moderate drinking was perfectly safe, which could leave many pregnant women confused. The college said that it would examine the new advice and decide whether to adopt it "in due course".

The change brings Britain into line with a growing list of countries which recommend abstinence. For years, the US, Canada, Australia and New Zealand have recommended that pregnant women abstain from alcohol. France joined them last autumn, saying that research had linked moderate levels of drinking and permanent brain damage.

Research from the Office for National Statistics has shown a sharp rise in fatal drinking habits among women. The study, of "preventable mortality", found that the annual rate of alcohol-related deaths had risen by two thirds between 1993 and 2005, to 1,873.

However, the statistics only refer to death certificates where alcohol-related conditions such as cirrhosis are specifically mentioned. Charities put the annual death toll for both sexes at about 22,000.

Ministers were moved to act over drinking in pregnancy after recent research found that 9 per cent of expectant mothers drink more than the recommended limit. Other data found that a quarter drink right up to the limit.

The existing advice to drink in moderation has been in place for about ten years. Previously, midwives regularly told pregnant women to drink up to eight units a week, and even recommended Guinness to prevent anaemia.

Heavy drinking can cause foetal alcohol syndrome, an incurable condition resulting in retardation, poor memory and, in the worst cases, facial abnormalities. About 1 in 1,000 babies are born with the syndrome each year worldwide.

But a milder condition, foetal alcohol spectrum disorder, is more common, affecting more than 6,000 children in Britain each year, and is a leading cause of learning difficulties.

Because many women do not realise that they are pregnant for the first few months, the advice was extended to those trying to conceive as well. It also states that should a pregnant woman choose to carry on drinking, she should not get drunk and keep to the previous recommendation of one to two units once or twice a week in order to minimise risks to the baby.