In a day or so, her doctors will have to consider if she is well enough to fly to Malta for two days of engagements on behalf of the Queen.
Kate is said to be eager to go, and her staff members at Kensington Palace are giving her as much time as possible before a final decision is made about traveling to the Mediterranean island Saturday. They are carrying on with the planning for the visit, according to palace sources.
At the same time they are also making contingency plans to send another member of the family – possibly her husband William – in her place to represent Queen Elizabeth II, who is 88.
Kate, 32, is suffering from Hyperemesis Gravidarum, which also struck her during her first pregnancy with Prince George in 2012. She is due to attend the official commemoration of Malta’s independence – set to be a landmark visit for her, following a personal invitation from the Queen to step into her shoes. Palace sources have called it a seminal moment in Kate's royal life.
But it appears Kate was not feeling well last weekend – it was widely reported that she did not travel and was looked after by her mother, Carole, while William was in Scotland with the Queen and Prince Charles.
Caitlin Dean, from the charity Pregnancy Sickness Support and the author of Hyperemesis Gravidarum: A Definitive Guide, would be surprised if Kate does go.
"It’s hard enough being in a car with this condition," she says. "A major part of managing the condition is making sure you are able to rest, and even if you can do short periods of being up and about, you have to rest afterwards.
"Feeling a bit better and then doing too much and relapsing is very common. Once you are feeling better, you want to get up and do things, particularly if you are a mother already, but you have to be careful not to relapse."
Veteran royal watcher and author Judy Wade says, "She will pay attention to her doctors, of course. But I’m sure she is torn between duty to the Queen and devotion to her baby son and the forthcoming child."