Britain's Catherine, Duchess of Cambridge made headlines recently when news of her pregnancy broke after she was admitted to hospital suffering from acute morning sickness. Morning sickness is an unwelcome side effect that can detract from the joy of pregnancy.
"Nausea and vomiting are one of the most common side effects of early pregnancy, affecting 70 to 80 per cent of all pregnant woman," says Dr Julia Dresel of the Kandang Kerbau Women's and Children's Hospital in Singapore. "The expression 'morning sickness' is misleading, since it is not a real sickness, but a feeling of nausea that can last throughout the whole day."
The degree of nausea and vomiting varies widely between women, and as in the duchess' case, can be so severe that it warrants a stay in hospital. While severe morning sickness occurs in women carrying both boys and girls, it is commonly associated with women carrying girls or multiple fetuses.
Severe morning sickness, or hyperemesis gravidarum, is defined by the loss of at least 5 per cent of total body weight and affects about one in 200 to 500 pregnant women. Weight loss occurs because of frequent vomiting and the inability to keep down food and liquids, leading to dehydration and malnutrition.
The condition can lead to medical complications and should be rapidly treated with anti-sickness medication and intravenous hydration. Before the introduction of intravenous treatment in the 1950s, severe morning sickness could prove fatal to both mother and fetus.
One rare complication that can arise is a neurological disorder known as Wernicke's encephalopathy. This occurs because of a lack of vitamin B1. Women who are admitted to hospital for severe morning sickness are typically given supplementation of this vitamin and electrolytes through intravenous hydration. Causes of morning sickness remain poorly understood but it is believed that several factors are involved.
One theory points towards high levels of the pregnancy hormone human chorionic gonadotropin that peaks during the first trimester, before falling after week 12. This hormonal change at the early stage of pregnancy coincides with the time when symptoms of morning sickness predominantly appear.
Another hormonal change that happens during pregnancy is a flood of progesterone that causes relaxation of smooth muscle, which includes the muscles of the digestive tract. Because of this, the passage of food slows down and can lead to nausea and vomiting after a large and heavy meal.
In addition, fatty and strongly flavoured foods are believed to induce feelings of discomfort.
On the other hand, low blood sugar levels, particularly in the morning after a long period without food, can also cause nausea. Some expectant mothers find relief by eating small amounts of food frequently throughout the day and in the morning before rising.
To avoid dehydration, pregnant women are encouraged to drink more fluids. But drinking plain water can become difficult because of changes in their sensation of taste.
Simple alterations such as adding lemon or orange juice to water to make it more palatable or drinking herbal teas are believed to help. Ginger is a common folk remedy for nausea that is used in Asia.
While not scientifically proven, wristbands that press on the acupuncture point pericardium-6, situated on the underside of the wrist between the two tendons, have been reported to relieve nausea.
Fortunately, while severe morning sickness cases can lead to complications for both mother and fetus, the milder morning sickness experienced by most women is not linked with a higher risk of miscarriage, or with a less robust pregnancy.
David Tan is a research scientist at the A*STAR Institute of Medical Biology, Singapore. He holds a PhD in stem cell biology from the University of CambridgeTopics: Kate Middleton