The couple, both 34, are already parents to two daughters - Juliette, 5, and Mackenzie, 2-and-a-half.
They always planned to add to their brood but their dream of a big family was almost cut short when Street was diagnosed with a rare and incurable auto-immune condition Churg-Strauss syndrome.
After almost two years of intensive treatment, Street is in remission - but the syndrome can reappear at any time without warning.
Last year she sat down with her doctor to discuss having a third baby and was told it was too risky with her condition.
Street and France tried to resign themselves to the fact they were not going to have more children - then a close friend offered to help.
"It's a massive thing for someone to do for you," said Street.
Friends and fans were quick to congratulate Street on social media, with journalists Alistair Wilkinson and Carolyn Robinson, and My Food Bag founder Cecilia Robinson among the first well wishers.
Street and France reveal the full details of their surrogacy journey in tomorrow's Weekend Herald.
Street is a host on the NZME breakfast show Sarah, Sam and Toni on The Hits radio station.
She also co-hosted TVNZ programme Seven Sharp along Mike Hosking, but left the role last year.
