Most cases of nausea and vomiting are regarded as mild, but the effect on pregnant women's sense of well-being and daily activities is usually underestimated. Hyperemesis gravidarum is the most severe form of nausea and vomiting in pregnancy and is defined as persistent nausea and vomiting leading to dehydration, ketonuria, electrolyte imbalance and weight loss greater than 5% of pre-pregnancy weight.

Nausea in pregnancy is reported in 50–80% of pregnant women; 52% of pregnant women experience symptoms of both nausea and vomiting during early pregnancy, and 28% experience nausea only. Reduced incidence is noted in smokers and in women who subsequently experience miscarriage. Hyperemesis gravidarum affects between 0.3% and 2% of all pregnant women.

Increased incidence of nausea and vomiting is associated with:

• Multiple pregnancies
• Mother or sister with nausea and vomiting in pregnancy
• Previous pregnancy with nausea and vomiting
• Hydatidiform mole
• Nulliparity
• Unplanned pregnancy
• Female gender of the fetus
• Non-smoking
• Low socio-economic status
• Younger maternal age
• Dependent personality trait
• Obesity
• Stress

Symptoms commonly start 4–7 weeks after the last menstrual period and cease by 12 weeks in 60% of affected women. About 9% of affected women have symptoms that persist beyond 16 weeks and may persist until 22 weeks of gestation. Symptoms often come and go and can occur at any time during the day. Typical symptoms include nausea, vomiting, fatigue, anorexia and weight loss (usually around 5% of pre-pregnancy bodyweight).

You can be reassured that nausea is a normal part of pregnancy and that pregnancy outcomes are generally better for women who suffer from nausea and vomiting in early pregnancy. Accept support from your partner, family and friends and rest as much as possible as tiredness can make nausea worse.

Nausea is thought to be caused by the changing pregnancy hormone levels. You can experience it at any time of day or night - not just in the mornings - and it is often triggered off by certain foods, like coffee and fried or spicy foods, or smells, such as perfume, cigarette smoke or petrol. It can also be caused by hunger.

Try eating small, frequent meals, once every two hours or so throughout the day, based on starchy carbohydrates. You could try:

• bread
• toast
• plain biscuits or ginger biscuits
• banana
• breakfast cereals
• plain crisps

Having something to eat like plain or ginger biscuits about 20 minutes before getting out of bed in the morning may help.

Eating cold meals rather than hot meals, which may prevent any smell-related nausea, as cold food does not seem to give off as much smell as hot food

Glucose tablets to possibly help prevent blood sugar levels from dropping (low blood sugar levels may cause nausea)

Avoiding any foods or smells that trigger symptoms

Avoiding drinking cold, tart, or sweet beverages

Avoiding caffeine and alcohol

Have lots to drink to avoid dehydration but drink little and often rather than large amounts this may help to prevent vomiting.

You may find it reassuring to know that, for most women, the last two thirds of pregnancy are relatively nausea-free. Very rarely, however, some women experience excessive or uncontrolled vomiting during pregnancy which can make them dehydrated. If this occurs, seek advice from your doctor.