Kate Middleton Pregnant: Duchess of Cambridge Feeling Better as Twins Speculation Grows

The Duchess of Cambridge, Catherine Middleton, who is pregnant with her first child, is improving having been diagnosed with Hyperemesis gravidarum, an acute morning sickness.

"The Duchess of Cambridge is continuing to feel better," a St. James's Palace spokesman said, "She and the duke are immensely grateful for the good wishes they have received. She will remain in hospital at present and will continue to be treated for hyperemesis gravidarum."

Hyperemesis gravidarum is a "potentially serious" ailment that entails vomiting and a bodily reaction against intake of food and liquids. This sickness, most commonly present in pregnant women carrying twins, could last up to the 21 week of pregnancy.

Prince William was spotted leaving the King Edward VII Hospital in central London dressed casually in a sweatshirt, chinos and trainers, and seemed happy after visiting the mother-to-be.

"There's a very good reason that pregnancies aren't normally made public until after a successful 12-week scan, so the couple obviously remain concerned," a royal source was quoted as saying.

Meanwhile, medical experts are suggesting that the royal couple could be expecting twins.

Dr. Ashley Roman, of New York University Langone Medical Center, told ABC Nightline that women carrying twins had a 7.5 percent higher risk of experiencing hyperemesis gravidarum.

"It's traditionally thought that nausea and vomiting is a sign of a healthy pregnancy," Roman said.

As the royal family, awaits its new addition, Prince William and his wife will move to a more "secure environment" in preparation for the baby, US Weekly reports. The two will reportedly make their permanent home in Apartment 1A of London's Kensington Palace, a four-storey, 20-room flat currently undergoing a £932082 ($1.5 million) renovation.

"Kate is keen to put her stamp on the place with things she's bought on her travels," a source told US Weekly, "She felt certain pieces would be nice 'when we have a bigger home.'"

Finally, click here to take a look at the best pcitures of royal parents-to-be...