The world is rejoicing because there’s another royal baby on the way! Kensington Palace released a statement announcing that Kate Middleton is pregnant and expecting her third child with her husband, Prince William. The Duke and Duchess of Cambridge and the rest of the royal family are overjoyed, but Kate had to cancel an appearance on Monday, Sept. 4 because she’s already struggling with a serious health condition early on in her pregnancy. Keep reading below to find out more about Kate’s battle with hyperemesis gravidarum — an acute and dangerous form of morning sickness.

What is hyperemesis gravidarum?

While morning sickness is common and affects 70 to 80 percent of pregnant women, it usually occurs early on in the pregnancy and subsides after a few weeks. Hyperemesis gravidarum, on the other hand, is a more severe form of morning sickness that causes dehydration, vitamin and mineral deficit, and weight loss through frequent nausea and vomiting, according to WebMD.

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The symptoms can be debilitating.

In morning sickness, women usually experience nausea that isn’t always accompanied by vomiting but with hyperemesis gravidarum, nausea is almost always accompanied by vomiting, according to the American Pregnancy Association. Also with hyperemesis gravidarum, the symptoms of nausea and vomiting do not allow affected women to keep food down and it causes severe dehydration.

Kate was hospitalized because of it in the past.

For her two previous pregnancies — with four-year-old son George and two-year-old daughter Charlotte — she had to seek treatment in different instances. Back in 2012, she was treated at London’s King Edward VII hospital for several days while she was in the early stage of pregnancy with Prince George. She also suffered from the illness during her pregnancy with Princess Charlotte, but she was treated for her symptoms at home at Kensington Palace.

Last month, Closer reported, Kate was rushed to the hospital in Marylebone, London where she was treated for an unknown illness and now it seems like it was because of hyperemesis gravidarum.

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