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. 

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.