An Australian woman has given birth to identical quadruplets, conceived naturally, after a pregnancy described as “extremely high risk” by the Royal Brisbane and Women’s Hospital.

The four girls, who were born by Caesarean section at 28 weeks and four days on July 14, were monozygotic quadruplets, where a single fertilized egg divides into four embryos.

The hospital said the girls’ mother, Jenitar Na’amoana, 34, and her husband Jortham, already had four children and were “immensely surprised” when they were told they were expecting quadruplets.

Dr. Alexa Bendall, who cared for the mother from the beginning of her pregnancy, estimated that identical quadruplets occur “in one in every 15 million pregnancies” and said that “but sharing the same placenta is unheard of.”

Bendall, who is an obstetrician and maternal-fetal medicine specialist, said that pregnancy was very high risk, and that the hospital admitted Na’amoana as an inpatient at 25 weeks so she could be monitored.

“We always said if we could get her to 28 weeks, we’d be fine,” Bendall said.

“So the fact that we have four beautiful, healthy babies born at 28 weeks and four days is incredible and we are so happy to be a part of it,” she added.