The Duchess of Cambridge, whose pregnancy the Royal Palace announced midday Monday, was admitted to King Edward VII Hospital in Central London for hyperemesis gravidarum, a very severe form of morning sickness.

"This is the extreme end of the bell curve," says Dr. Katherine O'Connell White, the Division Chief of the Obstetrics-Gynecology Department, General Obstetrics and Gynecology Division, Family Planning Section at Boston's Baystate Medical Center. "Some degree of nausea with or without vomiting happens within 50-90 percent of pregnancies. Hyperemesis gravidarum is the term for the extreme, which is roughly half a percent to 2 percent of pregnant women."

Women with hyperemesis gravidarum experience symptoms beyond the typical nausea associated with morning sickness. With hyperemesis gravidarum, women may feel dizzy upon standing, have trouble urinating frequently or pass dark-colored urine. They also begin to lose instead of gain weight.

"Most pregnant women can relate to the fact that weight gain starts about as soon as your pregnancy test is positive, so women suffering actually have the opposite problem," Dr. White adds. "It's never helpful to lose weight in pregnancy."


Medication and sometimes hospitalization is used to treat hyperemesis gravidarum.

"The hospitalization happens if you are vomiting so much that your electrolytes are imbalanced," Dr. White says, "meaning that your blood levels of sodium or potassium are too high or too low." She says that you also can develop keytones in your urine, "a sign that your body is burning through muscle because it doesn’t have enough calories coming in through what you eat."

Dr. White says that women in their first pregnancy are at a higher risk of developing hyperemesis gravidarum, as are women sensitive to hormones (those who get nauseas on the birth control pill, for example) and — rumor alert — women pregnant with twins. She adds that it usually manifests early, about five or six weeks into a pregnancy, and is gone at around 16 weeks. However, some women can still have symptoms into their third trimester and even up until their delivery.

Though the mother suffers with this condition, the baby is not at an added risk for complications.

"As long as she is treated for her dehydration, her pregnancy is not at risk, and in fact this might be a sign that her pregnancy is healthier," Dr. White adds.

Joined by husband Prince William at the hospital, Kate has canceled her next three official engagements, according to

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