Louisville (US) | An Australian woman has given birth to identical quadruplet girls after a pregnancy doctors described as incredibly rare.

Jenitar Sau Na'amoana, who is 34 years old and already had four children, delivered the babies last week at Royal Brisbane and Women's Hospital in Queensland state.

"We are very excited to be able to care for this amazing little family, a big family now," Dr. Alexa Bendall, a maternal fetal medicine specialist who cared for Na'amoana, said in an interview released by the hospital.

The babies were conceived naturally and came from one fertilised egg that split into four, "which was incredible," Bendall said.

"We think the figures are probably around 1 in 15 million for a case like this to be spontaneously conceived," she said. "We don't think it's ever happened in Australia." Overall, experts say, the chance of conceiving quadruplets naturally is only 1 in 700,000; most are conceived with the assistance of medical technology.

Hospital officials said Na'amoana and her husband, Jortham, hadn't planned to have more children and were quite surprised when she became pregnant with the quadruplets.

Na'amoana faced a high risk of complications, especially given the fetuses shared one placenta. In general, being pregnant with any multiple fetuses puts a mom at increased risk for problems such as pre-term birth, miscarriage and birth defects, according to Johns Hopkins Medicine.

Na'amoana was monitored by a large medical team at the hospital since 10 weeks gestation and was admitted as an inpatient at 25 weeks so she could be monitored, hospital officials said. She delivered the babies by cesarean section on July 14.

"The fact that we've got four beautiful, healthy babies born at 28 weeks and four days is incredible," Bendall said. "Mum did lose a little bit of blood but not an excessive amount for having quads, and she's doing well." The babies are doing well in the neonatal intensive care unit. Their names are Emily, Harriet, Catherine and Alexa, in honour of Bendall. The doctor called the name a "beautiful tribute," and said she feels privileged to have helped bring these children into the world.

"From an academic perspective, it's really interesting," she said. "But also from a human perspective, to be able to be part of the family's journey and come out with four beautiful babies and a healthy mum is very precious."