out of england twaud that rocketed around the world. The future queen, kate middleton, expecting her first child. But she was rushed to the hospital. Prince william by her side. Abc's lama hasan is there. We talked with sources inside the palace. She has the latest on what happened. Lama. Reporter: Good evening, diane. The couple had been so tight-lipped about the pregnancy that even those here at the palace the queen, prince charles and other members of the royal family reportedly only found out about it today. But when kate was hospitalized, the palace decided it was time to break the news to the world. The last time the world saw kate middleton was on friday, a picture of health playing field hockey. Now we learn the duchess of cambridge is pregnant and hospitalized for a condition called hyperemesis gravidarum. The palace today saying as the pregnancy is in its early stages, her royal highness is expected to stay in the hospital for several days and will require a period of rest thereafter. Hg is a severe form of morning sickness that debilitates 2% of xnts apartment mothers causing severe vomiting, weight loss and dehydration. Abc's sharyn alfonsi experienced it with both of her pregnancies. You are weigh not throwing up a couple of times a day, you're throwing up two dozen times a day. You can't keep anything down. Reporter: Kate is likely less than 12 weeks' pregnant. In most cases, the condition will ease after 16 weeks. Doctors say hg can also give a hint about the baby. Studies show mothers that experience it have slightly higher odds of carrying a girl or twins and if there are twins and there needs to be a c-section, doctors tell us it is clear that one will be delivered first and that's the first in line. Looking at the royal line of succession, there is the queen then charles, william then harry. But the rules of succession are changing, so whether will and kate have a boy or a girl, this new baby will now bump harry and 37 other members of the royal family and be the next in line after william. William's child will be third in line regardless of whether it's a girl or boy. Reporter: The ever since the fairy tale wedding 18 months ago, the world has been watching for a baby bump. And kate kept us guessing. There was this moment the duchess toasted with water and not wine on the couple's third official tour representing the monarchy. And this when william sparked speculation after accepting a baby gift. Harry serving in afghanistan was reportedly told of the news that he'll be an uncle by e-mail. As for katie, she'll remain in the hospital for several days. We read your questions online all day about this condition that sent kate middleton to the hospital, and we bring in now abc's dr. Jennifer ashton who delivered 1,000 babies. How big a risk is this to mother and child. This is potentially see serious authorize a pregnant woman. At this stage of pregnancy, however, most of the risks lie with the mother. How do you treat it? What do you do? It depends how sick the mother is. We usually modify the diet, bland meals, small frequent meals and she might be administered to the hospital where i.V. Hydration is given. If that doesn't work we go on to medications, very strong anti-nausea medications that work both in the brain as well as the stomach. If necessary, tube feedings with a permanent catheter might be needed. I know that you wanted to stress to everybody this isn't morning sickness as sharyn alfonsi said. This is I spectrum of different reaction. Absolutely right, diane. This is a much bigger deal than just queasiness. This is potentially very serious. She is getting great medical care. Thank you, jennifer ashton.