Because the condition can be due to a surge in pregnancy hormones and experts say this could be linked to twins, the big question is should Kate actually be carrying twins, which of the children will end up on the throne?
It would seem that if the twins were boys the first-born baby would succeed. Under new legislation, if Kate were to give birth to a boy and girl, it would be the first-born who succeeds, no matter their gender.
However, if a caesarean is necessary it can become more complicated. Alan Farthing, the royal gynaecologist would, in theory, make the decision as he would be performing the operation. But then the question is, would it be left to him? Would William make the decision?
Until Kate and William know for certain whether they are having twins we can only wait and see.