Earlier this month, a baby boy was born in Israel with a twin fetus. The rare episode was recorded by Asuta Medical Center in Ashdod.

“We were surprised that the swelling in the baby’s abdomen, which was identified by ultrasound before delivery, was caused by her twin sister’s malformed fetus,” Omar Globus, a specialist in neonatology, told the Times of Israel.

He explains that medical cases are rare and occur in about one in every 500,000 people registered. After delivery, doctors performed an X-ray and ultrasound examination of the baby’s abdomen.

They found that the embryo was not fully formed, but that it had developed some bones and a small heart. “But it doesn’t look like an embryo as you thought,” the specialist explains. “This abnormality occurs during fetal development when the chambers close, and one embryo surrounds the other,” explains Globus. “The internal fetus is partially developing, but not adapting to life.”

Doctors were able to successfully remove the defects in the girl’s abdomen, and the boy recovered at home with his mother.