Pregnant Kate Middleton is spending a second day in hospital today - Wiliam arrived earlier and the Middletons have left their home and are believed to be on the way - and there is a mass of speculation in the British papers that Kate could produce twins, on the basis that hyperemesis gravidarum (HG) - the acute form of morning sickness from which Kate is suffering – is more common in mothers to-be who will have a multiple birth than other women (it’s also, as Dr Kent Sepkowitz explains on the Beast, more likely to occur in cases where the developing fetus is a girl).
But what no-one on the British press seems to have yet latched on to is the fact that twins often run in families, and Kate and William’s bloodlines are stuffed full of twins. In fact many would see a family line of twins as a stronger predictor than HG.
As Robert Lacey wrote for the Royalist earlier this year, “Kate could very easily produce twins: William's uncle Charles Spencer has identical twin daughters; his grandfather Lord Fermoy was an identical twin; on Kate's side her paternal grandmother had a twin sister (Peter Middleton, Kate's grandfather, rather charmingly married one twin while his brother married the other) and Kate's father Michael had twin Middleton great-aunts.”
Twins have never been born into prominent positions in the British line of succession before, and royal baby twins would surely send the global fascination with the royals into overdrive.
Were the duchess to bear more than one child next year, the first to be born would take a higher place in the line of succession, regardless of sex.
The babies would become third and fourth in line to the throne, ahead of Prince Harry, as the ancient rule of royal primogeniture, which gave males precedence, was scrapped last year.
However, twins could yet present a major test for the newly-framed laws of succession – for what if the children were born by Caesarian section?
Last year, Crown Princess Mary of Denmark gave birth to twins, a boy and a girl. Before the birth, there was speculation that Mary would have a caesarean section delivery, leading to suggestions that the presiding doctor would effectively be choosing the babies’ position in the line of succession.
The babies were eventually delivered without surgery. The boy, Prince Vincent, was delivered around 25 minutes before his sister, Princess Josephine, and therefore took a higher place in the Danish line of succession.
The timing of the pregnancy led to speculation about where and when the baby was conceived. The fact that the Duchess is not yet 12 weeks pregnant means the baby could have been conceived during the couple’s tour of the Far East in September. The baby could be born near to the Duke’s 31st birthday on June 21.
The Duchess is reportedly being treated by Marcus Setchell, the former gynaecologist to the Queen, who delivered the Countess of Wessex’s two children as well as Leo Blair, the son of the former prime minister.
Kate is likely to be kept in hospital for a number of days. The Duchess had a number of engagements this week, including a visit to London's Docklands tomorrow for a charity fund-raising session on a brokers' trading floor, but they have all now been cancelled, said St James's Palace.