Kate Hill was told she may never conceive due to her polycystic ovary syndrome — but she ended up conceiving twice in 10 days, making medical history.

Kate went on hormones, and after having unprotected sex with her husband Peter, she ended up getting pregnant. She began ovulating again during her pregnancy, and conceived a second time 10 days later with the remaining sperm from their initial intercourse.

“We actually didn’t realize how special that was until they were born,” the Australia-based mom tells Today Tonight Adelaide. “Usually a woman doesn’t ovulate once they’re pregnant with all the hormones, but Charlotte was coming no matter what.”

Kate’s double pregnancy, called superfetation, is so rare that her OBGYN had never encountered it before. Today Tonight Adelaide reports that there are only 10 known cases of this happening before.

“I was shocked — shocked and happy, of course,” says Peter. “It was a hole in one!”

Now the non-identical twins, Charlotte and Olivia, are healthy 10 month olds with different blood types and different personalities.

“Olivia is pretty loud, but Charlotte is the demanding one,” says Kate. “They are definitely little miracles.”

This article originally appeared on People.com.