It was the news that the country has been so eagerly anticipating. On Monday, the British royal family, and the rest of the world, celebrated the happy news that the Duchess of Cambridge is expecting her second baby with Prince William.

It has been revealed that the pregnant royal is being treated for hyperemesis gravidarum - the severe morning sickness she also suffered while expecting Prince George.

But what is Hyperemesis Gravidarum? HELLO! Online takes a look…

Hyperemesis Gravidarum is a severe, and potentially dangerous, form of morning sickness where mothers-to-be struggle to keep down any food or liquid, which can lead to dehydration.

Unlike most morning sickness, it usually persists past the first trimester, up until around week 21 of pregnancy, although it can last much longer.

It affects fewer than four in every 1,000 pregnant women and is treated by giving fluids intravenously and anti-sickness tablets.

It is more often experienced by women expecting twins; mothers-to-be who suffer from the condition are three times more likely to have a multiple birth than other women.

As well as severe nausea, vomiting and food aversion, women suffering with hyperemesis gravidarum often feel tired, dizzy and confused. They can also lose around 10 per cent of their body weight.

Dehydration is the big danger with the condition and that can cause symptoms that include headaches and palpitations. Because the mother-to-be cannot retain food, there is also a risk of nutritional deficiencies.

The symptoms of hyperemesis gravidarum usually appear between weeks four and six of pregnancy and peak between weeks nine and 13. Most women will experience some relief between weeks 14 and 20, although up to 20 per cent may require care throughout the rest of their pregnancy.

The precise cause of hyperemesis gravidarum isn't known – it is thought to be linked to the rise in hormone levels – and as such it isn't possible to prevent it from occurring. It can however be treated successfully.

It tends to be more common in young mothers, women experiencing their first pregnancy and those carrying multiple children.

Women suffering from hyperemesis gravidarum in its early stages are advised to rest and eat small pieces of dry toast or crackers before getting out of bed.
Small frequent meals are also encouraged, although fried foods, or anything else that triggers nausea or vomiting are best avoided.

If symptoms are severe, the mother-to-be will be admitted to hospital for a few days for observation and to treat dehydration with intravenous fluids.

Research has shown no long-term harmful effects in mild cases. In more severe cases – fortunately very rare – there is a risk for mother and baby, particularly if the condition is not recognised and treated early on, including pre-eclampsia and premature labour.

This page is for general information only and should not be treated as a substitute for medical advice.

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