ST. LOUIS, Mo. (KMOX) – Prince William’s wife Kate remains in a London hospital, recovering from what is being called acute morning sickness. So what exactly is acute morning sickness?

SLU Care obstetrician Dr. Leslie McCloskey says acute morning sickness or hyperemesis gravidarum is when the traditional nausea and vomiting gets so severe, the mother can’t keep anything down and could become dehydrated.

It affects roughly 1 in 200 pregnancies and can leave women severely sick to the point where they’re vomiting upwards of 30 times a day.

McCloskey says Kate might be losing weight as well, and that’s “what would require someone to be hospitalized.”

Treatment is usually intravenous fluids to protect against dehydration and then medications to help control the nausea and vomiting once they leave the hospital.