Kate and Peter Hill are members of a very elite group: The Brisbane, Australia-based parents conceived their daughters 10 days apart. It’s a phenomenon called superfetation, and it’s so rare that there are only 10 reported human cases in the world. 

“They are definitely little miracles,” the mom of Charlotte and Olivia, 10 months, told Australia’s Today Tonight on November 9.

Dr. Robert Atlas, chairman of the obstetrics and gynecology department at Baltimore’s Mercy Hospital, explained the phenomenon in a 2009 interview with Time. According to Atlas, superfetation occurs when a woman continues ovulating after becoming pregnant and the second fertilized egg is able to implant itself in the lining of the womb. 

Though Kate and Peter had intercourse only once during that time period, his sperm stayed alive for 10 days to fertilize the second egg that she spontaneously released. Kate’s obstetrician, Dr. Brad Armstrong, from Greenslopes Private Hospital in Brisbane, had never seen anything like it before. “I could not find any literature in the medical review websites at all,” he revealed during an interview with Today Tonight. “I had to go and Google it.”


Initially, Charlotte and Olivia were given two different due dates, December 20 and December 30, but both were delivered two days before a planned cesarean section.

The Hills can trade stories with Julia and Todd Grovenburg. In December 2010, the husband and wife from Arkansas welcomed superfetation babies. “This is an unusual and rare condition, but the possibility is real,” Grovenburg’s obstetrician told KFSM-TV. “It can only be confirmed after delivery by chromosomal and metabolic studies on the babies. She was evaluated … for this condition and they confirmed the suspicion of superfetation.” 

Per Scientific American, superfetation is well documented in badgers, buffalo, mink and panthers. 

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