When Kate Hill of Brisbane, Australia, became pregnant with twins, she joined the ranks of just 10 other women in history—she got pregnant twice within a span of 10 days. It sounds crazy, but in an interview with Australia's Today Tonight, she explains her rare condition.
She suffers from polycystic ovary syndrome, which required her to receive hormone treatment in order to ovulate. After the hormones, she and her husband Peter Hill had unprotected sex just once, and they conceived. While already pregnant, Hill ovulated again and became pregnant with another child in the following days, despite having sex only once. His sperm apparently stayed alive long enough to fertilize an egg a second time.
Hill's condition, called superfetation, is apparently so rare that her ob-gyn couldn't even find medical literature about it on the internet.
According to the BBC, "Pregnancy normally stops the monthly cycle of ovulation but very rarely a woman can release another egg after conceiving. If this is fertilised it could also implant and develop into a healthy pregnancy."
Peter and Kate are now the proud parents of daughters born 10 months ago, who although are twins, were born with different blood types, different sizes, weights, and gestational developments.
"We actually did not realize how special that was until they were born," Hill told Today Tonight.
Her husband chimed in, "Hole in one, maybe.”
Follow Ali on Twitter.
This article originally appeared on Cosmopolitan.com. Minor edits have been made by the Cosmo.ph editors.