Superfetation: Mom Gets Pregnant With Twins... 10 Days Apart

The rare phenomenon is known as superfetation.

An Australian woman who conceived twins 10 days apart has stunned doctors.

This is remarkable for two reasons. At the time of her pregnancies, Kate Hill, from Brisbane, was receiving hormone therapy for polycystic ovary syndrome – a condition that meant she was unable to ovulate, thus giving her a high infertility rate.

Additionally, Hill only had unprotected sex with her husband, Peter, once, yet conceived her twins at different times.

So how did this happen? According to the medical community, the rare phenomenon of becoming pregnant while already expecting is known as superfetation. This occurs when a pregnant woman continues ovulating after conceiving, allowing for a different sperm to fertilize another egg.

In comparison, fraternal twins occur when a woman releases two eggs at the same time, while identical twins occur when a fertilized egg splits into two.

As a result of superfetation, Hill conceived twins, Charlotte and Olivia, 10 days apart. While the girls, who are now 10 months old, were born on the same day, they had different due dates and were born at different sizes, weights and gestational development. Yahoo reports that the twins also have different blood types.

“Superfetation is so rare that I could not find any literature in the medical review websites at all.”

“We actually did not realize how special [superfetation] was until they were born,” Hill told Australia’s “Today Tonight.”

“What makes this case even more rare, is that my husband and I only had intercourse one time,” she continued. “His sperm stayed alive for 10 days to fertilize the second egg released.”

Superfetation is extremely rare since women normally stop ovulating when they become pregnant. As a result, only 10 known cases of the phenomenon have been documented in the past. One case occurred in 2009, when Arkansas woman, Julia Grovenburg, first conceived her daughter Julia, and then two weeks later conceived her son Hudson, Time reports.

Because the phenomenon is so uncommon it even stunned (and stumped) Hill’s obstetrician, Dr. Brad Armstrong of Brisbane’s Greenslopes Private Hospital.

“Superfetation is so rare that I could not find any literature in the medical review websites at all,” he said.

Hill now calls her girls “little miracles.”


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