When Dr. Janelle Cooper, an OB/GYN, pulled into the parking garage of the hospital where she works in Annapolis, Maryland, and walked toward the building, she saw a man running and thought, "Oh, that's unusual."

She noticed "a truck that was parked in the middle of the street, and the doors were flung open," Cooper told CNN.

And then, she heard a cry from the backseat that pieced everything together.

"I'd know those screams anywhere," Cooper said.

'Instinct took over'

The running man was the grandfather of Elsa Antunez. He had rushed her to the Luminis Health Anne Arundel Medical Center.

He stopped the truck in the parking garage by an entrance which would have put Artunez only a few feet from the front desk, where she would have been transported by a wheelchair to the delivery unit.

But by the time the car was in park, it was too late. The baby was coming.

When Cooper reached the truck, the baby's head was already out.

"My instinct took over and I just jumped into action and delivered the baby," Copper said.

Jean Andres, the hospital's labor and delivery director, arrived at work a few moments later.

Andres heard the "very distinct scream" delivery room teams recognize instantly.

"I put my lunch bag down, called the team to let them know we had a delivery in the garage," Andres told CNN. "And I proceeded to assist Dr. Cooper with the delivery that she had performed."

Artunez gave birth to a healthy baby girl, Yesenia Patricia, and surprisingly for a first-time mother, the doctor noted, it went quickly. "She did really well."

Once Yesenia was born, Andres dried her off and kept her warm until the medical team came and took the family to a maternity room in the hospital.

"The fact that it was in a garage was very unconventional, but it was not chaotic," Andres said. "It was actually a very beautiful birth," she recalled.

And although Cooper has delivered thousands of babies, she said this time was different.

"I've delivered in different places around the hospital before, but never in the back of a pickup truck," she said.

Baby Yesenia isn't the first to be born in the medical center's parking garage, Andres and Cooper noted, nonplussed.

"We delivered a baby in the elevator this week," Cooper told CNN.