Twin Girls Conceived 10 Days Apart Due to Rare Phenomenon


An Australian woman who was told she could never become pregnant recently gave birth to twin girls. But in an even more surprising twist, the girls were conceived 10 days apart.

Kate Hill revealed to Australia’s Seven Network that she had been diagnosed in 2006 with polycystic ovary syndrome, a condition that prevented her from ovulating. She had been undergoing hormone therapy in order to treat her condition.

Credit: Today Tonight on Australia’s Seven Network
Credit: Today Tonight on Australia’s Seven Network

The treatment may have been more effective than anyone could have predicted. Hill was able to conceive twice within 10 days, despite the fact that she only had unprotected sex once within that period of time.

It’s extraordinarily rare for a woman to conceive another time while still pregnant. Most twins are either the result of releasing two eggs at the same time, or a fertilized egg splitting in two.

The twin girls — Charlotte and Olivia — were born different sizes, weights, and even had different blood types.

“We actually did not realize how special that was until they were born,” Hill told Seven Network. “What makes this case even more rare, is that my husband and I only had intercourse one time — his sperm stayed alive for 10 days to fertilize the second egg released.”

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Hill’s bizarre pregnancy is due to a rare phenomenon called superfetation. There are only 10 documented cases of superfetation in the world. In those rare cases, the second conception does not usually happen more than a week later.

“I’ve seen pregnancies that were spaced three days apart, and we don’t know if maybe the two eggs were fertilized at the same time, but just took longer to implant in the uterus,” Dr. Tomer Singer, obstetrician-gynecologist and director of reproductive endocrinology and infertility at Lenox Hill Hospital told the New York Daily News. “I’ve never seen a situation where a patient gets pregnant, and then 10 days later gets pregnant again in the same cycle. This is a very interesting case.”

Even Hill’s obstetrician, Dr. Brad Armstrong, had to search Google for more information about superfetation.

“[I’ve] never ever seen it before,” Dr. Armstrong said. “[It was] so rare that I could not find any literature on the medical review websites at all. I had to Google it.”

Hill’s husband, Peter Hill joked during their televised interview on Australia’s Seven Network. “Hole in one, maybe?” Mr. Hill said. “I was shocked and happy, of course.”

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Danielle Tarasiuk

Danielle Tarasiuk is a multimedia journalist based in Los Angeles. Her work has been published on, Yahoo! Sports, KCET, and NPR-affiliate stations KPCC and KCRW. She’s a proud Sarah Lawrence College and USC Annenberg alumn.