A woman in Mississippi who was expecting to give birth to triplets has delivered identical quadruplets.
Kimberly Fugate, 42, was in the delivery room when her doctor told her: "There are more feet."
The quadruplets - all girls - were born on February 8 at the University of Mississippi Medical Center in Jackson almost 13 weeks premature.
They are currently in intensive care.
The fourth girl had somehow been concealed from ultrasound imaging throughout Ms Fugate's pregnancy.
Dr James Bofill, professor of maternal foetal medicine, said in a statement released by the medical centre that the odds of spontaneous quadruplets are 1 in 729,000.
In the Fugates' case, the odds are even smaller because their girls split from a single egg, meaning the siblings are identical.
"Those odds are incalculable," Dr Bofill said.
The Fugates have named the babies Kenleigh, Kristen, Kayleigh and Kelsey, according to local news reports.
They already have a 10-year-old daughter and do not plan any more children.
"This is it," she told the Clarion-Ledger newspaper.
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