Kate Middleton's Hyperemesis Gravidarum Isn't Just Morning Sickness

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While the world is celebrating the upcoming arrival of Royal Baby #2, Kate Middleton is probably trying to keep her breakfast down. The Duchess of Cambridge is suffering from hyperemesis gravidarum, a severe form of morning sickness that she also had while pregnant with Prince George.

Though most pregnant women experience some form of morning sickness, hyperemesis gravidarum is far less common, and way worse, sending more than 50,000 pregnant women in America to the hospital each year.

Unfortunately for Duchess Kate, women are more likely to get hyperemesis gravidarum if they had it during their first pregnancy. The exact cause of the illness is unknown, but may be due to high levels of one pregnancy hormone spiking and triggering the part of a woman's brain that causes nausea and vomiting. Signs of the condition first appear four to six weeks into a pregnancy and peak between nine and 13 weeks, but about one-fifth of unlucky women have to continue treatment for the entire nine months.