Siobhan Anderson gave birth to her two twins (seen here) two different highways on her way to the hospital. (ABC SCREENGRAB)

A woman in New York gave birth to twin boys early Saturday morning — on two different highways.

Siobhan Anderson of Amityville, N.Y., went into labour a week early on Saturday and headed to the hospital, where she expected to give birth to her two baby boys, ABC News reports.

"You'd better not give birth on the Northern State Parkway," her mother warned her as she set off in the car at 7 a.m.

Instead, she gave birth on the Southern State Parkway in Long Island.

And then again on the Wantagh State Parkway.

Anderson said she felt a major contraction just after her husband pulled onto the Southern State Parkway. Then she felt a baby's head.

"She kept screaming, 'The babies are coming,'" husband Bryan told ABC. "I was like, 'I think we have time to at least get to the hospital.'"

But the couple was forced to pull over near the next exit and call 911. Paramedics arrived and loaded her onto a stretcher, thinking they could get her to the hospital on time.

No dice. She gave birth to Gavin outside the ambulance on the stretcher on the highway at 7:35 p.m.

Once baby No. 1 was out, the paramedics got Siobhan into the ambulance, with the goal of getting to the hospital to continue the labour.

But the ambulance soon had to pull over on the Wantagh State Parkway. Just a few minutes later, at 7:46 p.m., Declan was born.

When the parents finally made it to the hospital, they walked in with their babies in their arms.

"We were just in shock," Siobhan said. "I'm still in shock that it happened. I can't believe I was able to do that."