Boris Johnson with his partner Carrie Symonds in northwest England. File / AFP
Johnson, 55, and Symonds, 31, have also got engaged to be married.
The announcement means the Conservative Johnson will become the first British prime minister to marry in office for 250 years, the Telegraph newspaper said.
The Sun newspaper quoted a Downing Street source as saying "Boris and Carrie are both delighted at this news. They have both known for a while but have kept it under wraps until the pregnancy progressed."
"It partly explains why he has been lying low recently - although he works flat out and that won’t change. Carrie is thrilled and she will also continue to work on her environmental projects," the paper quoted the source as saying.
The former London mayor took office on Wednesday and swept out more than half the ministers who served Theresa May in the difficult closing months of her premiership.
The two leaders spoke on Thursday, and Macron’s talks with Johnson would be in regard to the demands of the European Union about Brexit, the official added.
Britain's leadership contest was rocked on Saturday by reports that police were called to a late-night "row" between frontrunner Boris Johnson and his partner, just hours before campaigning opened to win over grassroots Conservatives.
Thomas Massie posted the photo of himself and six members of his family, each gripping a gun on his Twitter handle, and wrote "Merry Christmas! ps. Santa, please bring ammo."
UAE-based tycoon MA Yusuff Ali visited a family in the Kerala port city of Kochi that came to rescue during a helicopter crash in which he had a narrow escape seven months back.
Initial investigations revealed that the victim previously declared through more than 10 videos on his personal account on TikTok his inability to reach a girl he loved and that he could not meet her because she was in her home country.
"The Kingdom of Saudi Arabia has granted approval for entry of individuals vaccinated with the Russian Sputnik V vaccine starting from Jan.1, 2022," the Russian Direct Investment Fund (RDIF), which financed the development of Sputnik V, said in a statement.