"Rich and I are very excited to announce that we are expecting our first baby later this year," Gemma McCaw posted on Instagram last week, along with a photo of a tiny pair of Adidas running shoes between a men's and women's pair.
Richie's manager Dean Hegan was among family and friends to congratulate the pair in person.
"I told them I'm thrilled, couldn't be happier," he said.
"They are out of the country at the moment having a well-deserved few days off."
More than 900 messages of congratulations have flooded in since Gemma, a former Black Stick, posted the announcement.
Fellow All Black legend Dan Carter's wife Honor was among those congratulating the pair.
"Congrats Gem! Exciting times," she wrote.
New Zealand and South African netball champion Irene van Dyk wrote: "Let the fun and games begin! Best present ever."
Bachelor winner and Heartbreak Island host Matilda Rice said: "Yay! Exciting! Also this baby will be the best athlete NZ has ever seen with your guys' genes."
Media personality Nadine Higgins agreed, saying: "That Bub is going to come out of the womb running. I'm sure!"
Paralympian Sophie Pascoe wrote: "Amazing news! Congratulations Gem and Rich!"
Injured triathlete Terenzo Bozzone sent his wishes from his hospital bed after being hit and seriously injured by a truck earlier this month.
Laura McGoldrick, wife of cricketer Martin Guptill, was another to send her congratulations: "What exciting news. It is the best."
Toni Street said, "Yeeow! Best news Gem, so excited for you and Rich ... 2018 is a great year to have babies."
Gemma and Richie married in a lavish wedding in Wanaka in January last year.
Gemma, 28, was a member of the Black Sticks from 2008 until after the 2016 Olympics, when she decided to take a break. During her career she competed in three Olympic Games.
McCaw played 148 test matches for the All Blacks and was captain for 110 of those. He led the team to two Rugby World Cup victories and is the most capped test rugby player of all time.
He made his debut for the All Blacks at the end of 2001 and retired at the end of 2015.
Since then he has pursued his other passion of flying. Ritchie is an owner and director of Christchurch Helicopters.