Taranaki District Health Board says it is investigating why an ambulance arrived four hours later than expected in the remote settlement of Tahora.
The ambulance Annie Fletcher's husband called at 9pm on Saturday after she suffered painful back spasms did not arrive until 2.30am
Board spokesperson Joy Farley apologised for the delay, saying it was an honest mistake by the driver, who found two references when he looked up a map.
Ms Farley says the board will give the driver more training on how to use GPS and how to navigate around rural roads.
Robert Fletcher says he was told the ambulance would arrive in 90 minutes but it took five and a half hours because the ambulance driver got lost and drove 50km past their home.
Ian May, the health board's ambulance manager, has admitted there was a significant delay and says the board has apologised to the Fletcher family.
The Ambulance Association for the Central region says a dispatcher should have been helping the driver.
President Graham Hayward says he is surprised the ambulance did not have a GPS unit. Ms Fletcher says ambulances should be equipped with the units.
The incident is the second second ambulance error in the region since 2008.