Up to 85 per cent of women experience nausea during pregnancy - and half of these actually vomit.
But although morning sickness is thought to be linked to rising levels of some pregnancy hormones, the exact causes are unknown.
Common so- called remedies include vitamin B6, antacids and sugar solutions, all available over the counter from a chemist.
Women can also take antihistamines, but they must be prescribed by a doctor. Increasingly, mothers-to-be are also turning to remedies such as acupuncture and acupressure wristbands, which are often used to treat seasickness.
Some also take ginger, on its own or in food or tea, which is thought to cure nausea.
But there may be a silver lining.
Research has suggested morning sickness can help ward off breast cancer. In 2007, U.S. scientists found those who had it are 30 per cent less likely to develop the disease than those who had no nausea.
Jane Munro, of the Royal College of Midwives, said: 'It is disappointing. However, there is some limited evidence on the effect of ginger, acupressure and some antihistamines - as recommended in NICE guidelines - and vitamin B6.'