Kate Middleton Is Suffering From Hyperemesis Gravidarum. What Is That?

Kate Middleton, also called the Duchess of Cambridge, is pregnant with her third child, Kensington Palace said Monday. Middleton and her husband, Prince William, Duke of Cambridge, have not yet revealed a due date for the child.

As with her previous two pregnancies, Middleton is suffering from a severe form of morning sickness called hyperemesis gravidarum, which prevented her from attending engagements on Monday.