There is reluctance to use pharmaceutical products in pregnancy due to Thalidomide, the 1960s anti-nausea drug which led to birth defects.

But there is little evidence to suggest that alternative therapies have any real impact, the international group of researchers Cochrane found.

Campaigners say women who suffer receive a "Cinderella service".

Despite its name, the vomiting and nausea of morning sickness can occur at any time of the day and affect about half of pregnant women.

About two in 100 will experience it so badly they need to be hospitalised.

Ginger biscuits

Cochrane researchers looked at nearly 30 strictly controlled trials involving more than 4,000 women who were up to 20 weeks pregnant.

They examined six studies of acupressure and two of acupuncture, and found these methods offered no significant benefit.

One study of acustimulation - the mild electrical stimulation of acupuncture points - did document some improvement.

There was limited evidence for ginger, which is used in various forms from biscuits to tablets, or for vitamin B6.

There was also little evidence on the efficacy of antihistamines and anti-vomiting drugs including Debendox, which was withdrawn from the market in the UK but is routinely prescribed in Canada.

That does not mean these methods do not work, but that women - and health professionals - do not have any reliable evidence on which to make their judgements about the best treatments.

In the UK, there are currently no pharmaceutical products specifically licensed for use with pregnant women, but doctors who do prescribe for severe sickness tend to offer the antihistamines promethazine and cyclizines.

"Despite the wealth of different treatments available, it is not possible currently to identify with confidence any safe and effective interventions for nausea and vomiting in early pregnancy," said lead researcher Dr Anne Matthews, of the School of Nursing at Dublin City University.

"The difficulties in interpreting the results of the studies highlight the need for further, more rigorous trials in this area."

Dr Brian Swallow, a health psychologist and member of Pregnancy Sickness Support, said: "At present treatment varies according to the woman's geographical location.

"Some areas are very good, whereas others have not developed appropriate treatment protocols. There is very little research that that aims to help women with nausea and vomiting in pregnancy.

"In terms of treatments, the most effective appear to be anti-nausea medication. GPs are often reluctant to administer them because they are fearful that they may have harmful effects on the foetus - although there is no evidence to suggest that they have."