Kate Pregnant: Severe Morning Sickness Explained

The Duchess of Cambridge was admitted to hospital with a rare condition that causes severe morning sickness.

The severity of the vomiting caused by hyperemesis gravidarum can lead to dehydration, weight loss and a build-up of toxins in the blood or urine called ketosis.

Sky's Health Correspondent Thomas Moore said: "The first step would be to get a woman on to a drip as soon as possible, get some fluid back into her bloodstream.

"If that doesn't settle things, doctors can in fact stick a tube all the way through the stomach into the small intestines to make sure there is some nutrition getting into the mother.

"There would also be the possibility of medication."

Hyperemesis gravidarum affects 3.5 per 1,000 pregnant women and can cause women to vomit blood.

Hyperemesis gravidarum sufferer Jennifer Burner told Sky News: "I think what makes it so difficult is that not many people understand it. What you are going through is deemed by many people as normal, they just think you are being sick quite a lot.

"I was sick over 35 times a day, every day until the 35th week of my pregnancy, which means you lose weight. In my case I was put on drips to be rehydrated, put on steroids to keep my body warning.

"I have never had normal morning sickness but I don't believe it is quite like that."

Retired midwife Val Clarke told Sky News "It often happens in very slim young ladies who - I don't know the reason why - become pregnant and the demands of the pregnancy are overwhelming to the point that vomiting becomes much more severe much earlier.

"Poor Kate, it would appear she is having very early symptoms which are very severe.

"It is not anything that needs to be worried about, although in extreme cases sometimes termination is required because the mother becomes very, very ill and dehydrated.

"I admire Kate. She was playing hockey, she may have been feeling awful, but she put on a very good show for everybody. But now I think she needs to tend to her own wellbeing and that of the baby."

The condition usually passes after the first 16 weeks of pregnancy, but may also last longer.