6 December 2012 Last updated at 09:29 ET

Royal pregnancy: Duchess leaves hospital

The Duchess of Cambridge left hospital with husband Prince William

The Duchess of Cambridge has left hospital after several days of treatment for acute morning sickness.

Catherine, holding a bouquet of yellow roses, left King Edward VII hospital in central London on Thursday morning with her husband, Prince William.

Less than 12 weeks pregnant, she was admitted with acute morning sickness - hyperemesis gravidarum - on Monday.

St James's Palace said in a statement that she was now heading to Kensington Palace for a period of rest.

Her first child will be third in line to the throne, and will become monarch, whether a boy or a girl, after changes to the succession rules.

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Catherine smiled at the media, which have been assembled outside since her admission, when she emerged from the hospital.

She nodded when asked by reporters if she was feeling better.

BBC royal correspondent Luisa Baldini said the duchess seemed tentative and less energetic than usual.

A public announcement of the duchess' pregnancy, before the usual three-month mark, was prompted by her medical condition.

St James's Palace added: "Their Royal Highnesses would like to thank the staff at the hospital for the care and treatment the duchess has received."

Analysis Peter Hunt Royal correspondent

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As the pregnancy progresses, William and Kate face another challenge in the coming weeks.

The prince with a destiny to fulfil one day has to decide what to do in the meantime.

His current stint as an RAF search and rescue pilot, based in Wales, is coming to an end.

The remoteness of Anglesey, which was attractive to them when they were newly-wed, poses problems once they have a family and her relatives are some distance away.

William could move to another search and rescue base; pursue a different career in the military; or surprise, once again, the royal experts with an imaginative solution to the problem of what to do with the second-in-line to the throne.

The fourth option, becoming a full-time royal, is the one the 30-year-old is reluctant to embrace.

He knows what awaits. He doesn't want to rush there.

• Read more from Peter
• Severe morning sickness can be 'traumatic'

Catherine's father-in-law, the Prince of Wales, said he was "thrilled" at the pregnancy.

"It's a very nice thought to become a grandfather in my old age," said the 64-year-old heir to the throne, at HMS Belfast in London, where he was visiting the vessel which will accompany Sir Ranulph Fiennes' Antarctic expedition.

Catherine's discharge from hospital comes the day after it emerged that two Australian radio DJs impersonated the Queen and the Prince of Wales to dupe hospital staff into giving an update on the duchess's condition.

The hospital said confidentiality was taken seriously and telephone protocols are under review.

2Day FM said it was surprised their call was put through but "sincerely apologises".

The Australian Communications and Media Authority said it has received complaints about the prank call.

The privacy provisions of the commercial radio codes of practice apply to news and current affairs programmes, it said, but added that it had no further comment to make.

Catherine is not expected to attend any scheduled engagements for the time being, but Prince William will continue with his royal duties, including two events at the weekend.

It is not uncommon for pregnant women to experience morning sickness, particularly during the first few months of pregnancy, but some women (around one in every 200) experience severe nausea and vomiting, which continues throughout.

This condition is known as hyperemesis gravidarum or HG and needs specialist treatment and often requires a stay in hospital.

The main danger is dehydration - it can be difficult to keep enough fluid down orally, and doctors can treat HG with medication to help ease the nausea.