Kate Middleton's bout of exceptionally strong morning sickness unveiled her pregnancy and unleashed a floodgate of media speculation on the heir to the throne. Among the questions: Who will be next in line if Middleton has twins?

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Because Middleton's acute form of morning sickness, hyperemesis gravidarum (HG), has been linked to a greater likelihood of having twins, and because both Kate and Prince William come from families with twins, the question may prove relevant.

If Middleton has a vaginal delivery, the answer is clear: first-born equals first in line. A Caesarean-section complicates matters slightly; still, the first baby the doctor lifts out will one day become king or queen.

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After the Daily Telegraph first raised the question of a multiple birth, which would be a first in prominent positions in the British line of succession, some bookmakers lowered their odds on royal twins from 50/1 to as 8/1. Betting is also heavy on female names, perhaps because there is also an association between HG and girls (Victoria, Elizabeth, and Diana are among the favorites).

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"Unless there are two doctors lifting the babies out simultaneously, one will be first," Ingrid Seward, editor of Majesty magazine, told the Daily Mail Online. "I expect the twin who isn't out first would have more fun — they'd be the Prince Harry…That's why it's hereditary. It's a job, a duty — you don't do it by choice, it wouldn't work. One twin has to be there first – and you can't argue with that."

Last year in Denmark, Prince Vincent was born 25 minutes before his twin sister, earning him a higher place in the line of succession.

Photo: Kate Middleton in October/Credit: Corbis