In an Instagram post Carrie Johnson also said she had a miscarriage earlier this year. She wrote: “Hoping for our rainbow baby this Christmas.
“At the beginning of the year, I had a miscarriage which left me heartbroken. I feel incredibly blessed to be pregnant again but I’ve also felt like a bag of nerves.”
Mrs Johnson added: “Fertility issues can be really hard for many people, particularly when on platforms like Instagram it can look like everything is only ever going well.
“I found it a real comfort to hear from people who had also experienced loss so I hope that in some very small way sharing this might help others too.
A “rainbow baby” is a child born after a miscarriage, stillborn or neonatal death.
Ruth Bender Atik, national director of the Miscarriage Association, said it was “significant” that the two announcements were made at the same time.
She told Sky News: “When you a pregnant after a loss it doesn’t mean that you forget the heartache or the difficulty and distress that you had before.”
“Not everyone wants to talk about their experience of miscarriage, they may feel it is private to them or they are just comfortable talking about it. They might worry that people may say the wrong thing,” she added.
“But also it is important to talk about pregnancy after loss because it can be a very anxious time. A lot of people say that they lose the innocence and optimism they had the first time round because they concerned something might go wrong this time.
“For most people it doesn’t but it is still an anxiety.”
The prime minister, 57, tied the knot with Carrie Johnson (nee Symonds), who is 33, in a small ceremony at Westminster Cathedral in May.
Mrs Johnson previously used Instagram to announce the name of her first son, Wilfred Lawrie Nicholas Johnson – with the name Nicholas chosen in a nod to the two doctors who saved the prime minister’s life when he had COVID-19.
The baby was named after the prime minister’s grandfather, Wilfred, and his mother’s grandfather, Lawrie, as well as the two doctors, Dr Nick Price and Professor Nick Hart, who treated him in intensive care.
Wilfred was the fifth child known to have been born to a sitting prime minister.
Tony Blair’s wife Cherie gave birth to son Leo in May 2000, three years after her husband’s first election victory, and David Cameron and wife Samantha welcomed daughter Florence in 2010.
Lord John Russell, who served as the prime minister twice between 1846 and 1852, and again between 1865 and 1866, was the first PM to father a child while in office, having two during the late 1840s.