Carrie, 32, who is due to give birth late next month or in June, is getting regular phone and video calls from friends trying to keep her spirits up.
The conservationist, who says she is “on the mend”, has not seen her other half for weeks.
She is thought to be at the couple’s home in Camberwell, South London, just a few miles from St Thomas’ Hospital in Westminster where her husband-to-be is being treated.
She is banned from visiting him. No10 would not say if the PM is allowed to phone her.
A spokesman said: “He is in the intensive care unit and will be guided by the doctors as to what he can do at all times.”
On top of the PM’s desperate predicament, Carrie is trying to cope alone with the anxieties of becoming a first-time mum.
She also has to keep away from her own mum, Josephine, 72, who is in a high-risk category. The Queen has sent best wishes, and told Carrie she and Boris were “in her thoughts”.
Jemima Goldsmith, sister of Carrie’s good pal and life peer Zac Goldsmith, said it must be a “terrifying time” for her.
Carrie, who has so far kept silent on the PM’s condition, has Downing Street dog Dilyn for company.
On his Instagram account, the mutt left the message: “Wishing Dad a speedy recovery. My main task is looking after Mum whilst he’s away.” Another adds: “I know he is in the best place and receiving the best care.”