An Alabama woman with a rare congenital anomaly that results in her having two uteri has given birth to healthy twin girls.

Kelsey Hatcher and husband Caleb welcomed Roxi Layla on Tuesday night and her sister Rebel Laken on Wednesday morning at the University of Alabama at Birmingham Hospital (UAB), the mother-of-five announced on social media.

"Our miracle babies were born," Hatcher wrote on Instagram.

"They decided they were rare enough statistically that they should just go ahead and have their own birthdays too."

Hatcher has a rare double uterus and was pregnant with a baby on each side, a rare pregnancy known as a dicavitary pregnancy that has a one in a million chance of occurring.

"I had already taken care of Kelsey through her third pregnancy and knew she had a double uterus, but that was only one baby - two babies in two uteri were a true medical surprise," Hatcher's obstetrician Shweta Patel said in a hospital news release.

Hatcher's pregnancy was considered high risk and she was induced at 39 weeks.

After a combined 20 hours of labour, the two baby girls were born.

Although a typical twin pregnancy is defined by two babies in one uterus, Richard Davis, the physician who co-managed the pregnancy, said it is "safe to call the girls fraternal twins".

The first baby was delivered vaginally, as were Hatcher's previous three children, while the second one was born via C-section.

The medical team had come prepared with three potential scenarios for the delivery: both babies delivered vaginally, one baby born vaginally and one via C-section, or a C-section for both births.

"I can't wait to share the entire birth story with you guys," Hatcher wrote on social media.

"While we are all home now, we will take the time (to) bond, recover, and enjoy the holidays."