With both pregnancies, Kate has suffered from hyperemesis gravidarum also known as acute morning sickness - a condition that has been linked to multiple births. This has sparked even more speculation suggesting she is expecting twins.
On Monday night, the twins rumour became so prevalent that it caused all betting on the royal pregnancy to be suspended.
Bookmakers William Hill refused to take any bets on William and Kate having twins as the odds dropped to 9/1 before a suspension on betting at 9.43pm, reports the Express.
"We have had a load of unexpected bets including a large number of new accounts - with any other market I would say that people know," Rupert Adams, a spokesperson for the brand told the newspaper.
If Kate does have twins, it will be a first for the mother of a royal baby since the fifteenth century.
This latest pregnancy news comes after it was confirmed Kate would return to public engagements in the autumn.
A spokesperson said to the Daily Mail, "There will be engagements in October and November. We just haven't announced them yet."
Over the weekend of 20 September, the duchess was forced to pull out of a planned trip to Malta to celebrate the former British colony's 50th anniversary of independence on a two-day tour.
Prince William stepped in instead, and offered health updates about his wife to well-wishers while he was there.
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