News that the Duchess of Cambridge is expecting has been dampened by her hospitalisation for "extreme morning sickness" – but experts say the condition could mean even more exciting news.
Catherine is receiving treatment at London's King Edward VII Hospital for hyperemesis gravidarum, an acute morning sickness which requires supplementary hydration and nutrients.
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Professor Tim Draycott, an obstetrician at the University of Bristol, told Reuters the condition could indicate more than one royal baby may be in the offing.
"Hyperemesis is slightly more common with twins," Draycott said.
The condition affects around 2 percent of pregnant women and is thought to be caused by higher levels of the pregnancy hormone human chorionic gonadotropin, which can increase when there is more than one fetus.
The 30-year-old duchess is less than 12 weeks pregnant, according to a royal spokesperson, and Draycott said her condition posed little danger to her or the royal heir, provided she remains under medical observation.
Prince William addressed media and said his wife was likely to remain in hospital for several days. There was no detail about when the baby was due, although the prince's spokesman said she was less than 12 weeks pregnant indicating a UK summer birth.
"I'm delighted by the news that the Duke and Duchess of Cambridge are expecting a baby," UK Prime Minister David Cameron said on Twitter. "They will make wonderful parents."
Normally the condition is expected to last only 14 to 16 weeks into the pregnancy, but has been known to last until birth, leading to nutrition problems for the fetus.
A US study released this year surveyed 395 women with hyperemesis gravidarum and found a restrictive diet prior to pregnancy more than doubled the risk of prolonging the condition.
"Four factors prior to pregnancy were significantly different between HG lasting less than 27 weeks and HG lasting more than 27 weeks. These factors include allergies, a restrictive diet, greater weight, and younger age," the study concluded.
"In this study, participants with prolonged HG were almost five-fold more likely to be on a lactose-free diet due to self-reported lactose intolerance and twice as likely to be vegetarian."
The study said the prolonged condition could lead to low birth weight, decreased cognitive function and heart conditions.