A woman gave birth in her car then shoved the baby in a trash bag and drove home with it on the floor where she left it until it was found dead by cops a day later, authorities have revealed.

Part-time gym employee Brennan Hailey Geller, 21, is accused of concealing her pregnancy and giving birth in her car on Friday.

None of her friends in Lexington, South Carolina, or her parents appeared to have been aware of the pregnancy.

Brennan Hailey Geller allegedly gave birth in her car then put the baby in a trash bag and drove home with it on the floor where it died

The high school graduate allegedly gave birth in her car then stuffed the child into a trash bag.

Police said she then placed the rubbish bag containing the baby in the footwell of her car and drove home.

It was not until the next day, Saturday, that she sought medical attention, and doctors were immediately concerned when she arrived in the emergency room.

She told doctors nothing about the baby and authorities only discovered what happened when officers found the body in her car.

She faces more than 20 years jail after she was charged with homicide by child abuse when authorities found the infant's body

She faces more than 20 years jail after she was charged with homicide by child abuse when authorities found the infant's body.

The 21-year-old was only arrested after she was treated at hospital in Lexington, South Carolina, on Saturday for blood loss.

'The medical team caring for Geller told investigators she never told them the baby was in her car,' Lexington County Sheriff Jay Koon said.

She works at MUV Fitness and as a server at Travinia Italian Kitchen & Wine Bar, both in in Lexington, according to Facebook.

Geller gave birth on Friday night and the body was not found until hours after she went to the hospital on Saturday morning.

The report did not say how the baby died, but a newborn would struggle to survive while stuffed in a bag overnight.

Geller, who has no criminal record, is awaiting a bail hearing at the Lexington County Detention Center after her arrest on Monday afternoon.

A 2015 graduate of River Bluff High School, she works at MUV Fitness and as a server at Travinia Italian Kitchen & Wine Bar, both in in Lexington, according to Facebook.

Geller was largely raised by her mother Julie after her father Mike died in 2008.

She appeared to be keeping her pregnancy secret from those she knew as several people who claimed to be her friends expressed their shock online.

'And to think i was friends with her… I didn't even know she was pregnant,' one said.

'I didn't even know she was like this or even pregnant. Jesus, I can't believe this. I'm, like, shook (sic) to the core,' another said.

'Known her since grade school and never thought in a million years she would do this, I feel so horrible for the baby and the dad. I wonder if he even knows…'

South Carolina has 'safe haven' laws that allow mothers to legally abandon babies at fire stations, churches, and hospitals.