This doctor was about to give birth, when she swooped in to deliver another woman's baby.

After years of helping bring lives into the world, obstetrician/gynecologist Dr Amanda Hess was just hours away from welcoming her own second baby.

She was already dressed in her hospital gown on July 23 at Frankfort Regional Hospital in Kentucky, USA, and was preparing to be induced when she heard a commotion down the hall.

Fellow patient and mother-to-be Leah Halliday-Johnson, preparing for the birth of her fourth child, was in distress.

The 38-year-old was only 1cm dilated when she checked into the hospital. But after an hour, her baby was arriving faster than expected and the umbilical cord was loosely wrapped around the girl’s neck.

The nurses told her not to push as the on-call doctor was still on his way back from his break.

Leah Halliday-Johnson welcomed her fourth baby, a girl, with the help of Dr. Hess. Image via Facebook.

"I was not being quiet about the fact that it was difficult for me not to push," Leah told PEOPLE Magazine.

Despite the fact her own contractions were just minutes away from starting, Dr Hess knew there was no time to waste and she had to help Leah deliver her fourth baby.

"I just put on another gown to cover up my backside and put on some boots over my shoes, to keep from getting any fluid and all that stuff on me, and went down to her room," she told WKYT News.

It was then that she realised she had actually met Halliday-Johnson just a week earlier at her final pre-natal appointment.

Halliday-Johnson wasn't told until after her baby was born — a healthy baby girl — that the OBGYN wasn't on duty and was actually in hospital, preparing to give birth herself.

Dr. Amanda Hess with her own newborn daughter. Image via Facebook.

"I said, 'OK, it's great to see you. Can I push now?'" Halliday-Johnson told PEOPLE.

"She was in complete doctor mode. She just heard somebody needed help. She's a really special person. I'm thankful for her."

Dr Hess later welcomed her own baby, a girl named Ellen Joyce, who joins big sister Kate.

She joked that she thought taking a call the day before was "working up to the last minute."

"This was literally 'til the last second," she told LEX18 News.

LISTEN: What happens after you take your baby home from the hospital for the first time.