Britain's Prince William and wife Catherine are expecting their first child, but her severe morning sickness was attracting the most questions Monday.
The Duchess of Cambridge has been hospitalized for severe vomiting, called hyperemesis gravidarum, according to St. James's Palace.
While the condition doesn't typically endanger mother or child, "it is pretty miserable," says Kecia Gaither, director of maternal fetal medicine at Brookdale University Hospital and Medical Center in Brooklyn, N.Y.
Less than one per cent of all pregnant women are hospitalized for vomiting, says George Macones, an obstetrician-gynecologist at Washington University in St. Louis and a spokesman for the American College of Obstetrics and Gynecology.
Hyperemesis is slightly more common in twin pregnancies.
The college advises women who can't keep anything down for 24 hours or more to call their doctors. In severe cases, such as Catherine's, women can become dehydrated because of lack of fluids.
These women may need to be hospitalized for a few days so doctors can administer intravenous fluids, as well as anti-nausea medications, such as vitamin B6, a drug called Zofran or others, Macones says.
Doctors may also need to give these women potassium or other electrolytes to restore their normal balance, Gaither says. In "exceedingly rare" cases, women may need to be cared for in the intensive care unit. Doctors can typically intervene early, however, to prevent serious complications.
In most cases, nausea and vomiting go away by the second trimester, or about 13 or 14 weeks into the pregnancy, Macones says. A few unlucky women may have severe vomiting throughout pregnancy and require intravenous nutrition.
It's a condition that has few long-term consequences for the baby, said Tim Draycott, a consultant obstetrician for the U.K. Royal College of Obstetricians and Gynecologists and a specialist on Catherine's illness.
But, he added, it's miserable: "Poor her."
Doctors believe the cause of nausea and vomiting during pregnancy is rapidly rising blood levels of a hormone called HCG, or human chorionic gonadotropin, which is released by the placenta, according to the U.S. National Institutes of Health.
Across Britain, there were expressions of concern for the health of the duchess, laced with hopes her illness would not foreshadow months of difficult pregnancy. The Telegraph reported her condition had forced the Royal Family to accelerate the announcement, which was initially planned after she passed the 12-week mark. Royal officials would not disclose how far along the duchess is in her pregnancy.
-- USA Today