Kim Fugate looks in on Kristen, one of her four identical quadruplets. (University of Mississippi Medical Center)
Jackson, MS. (ABC) -- Kimberly Fugate, exhausted after an intensive labor and grueling cesarean section delivery of identical triplets, was ready to breathe a sign of relief, but the Mississippi mother's doctor had a surprise for her.
"They had got the three out and they said, 'More feet,'" Fugate said. "'More feet' ... that's all I heard and I said, 'Nooo!'"
A fourth identical quadruplet had somehow been missed by numerous ultrasounds, managing to keep her existence hidden until she popped out behind three of her identical sisters last week at the University of Mississippi Medical Center.
The Fugate four, named Kenleigh Rosa, Kristen Sue, Kayleigh Pearl and Kelsey Roxanne after family members, arrived three months earlier than expected, and just a day before their mother's 42nd birthday.
All four are currently doing well in neonatal intensive care after being born nearly 13 weeks premature. The girls will need to remain in observation, but Kimberly says she hopes to have them out by early May, on their original due date.
Dr. James Bofill, a professor of maternal fetal medicine at the hospital said the odds of conceiving identical quadruplets is astonishingly rare, especially in a case like Fugate's, where she became pregnant without the use of fertilization drugs or treatments.
"The odds of spontaneous quadruplets is one in every 729,000 live births," Bofill said. "The chances of having identical quadruplets [are] almost incalculable."
Kimberly Fugate and her husband Craig are also parents to another daughter Katelyn, 10. The pair have set up a Facebook page to keep relatives updated on the quadruplets' progress.
In January a California mother gave birth to identical triplet boys six weeks earlier than expected. They were also conceived naturally, although there were no surprises for the parents in that case.
Doctors told ABC News at the time that a shortened gestation time is common for multiples and many triplets are born earlier than expected, during the 32nd rather than recommended 40th week.
In 2007, ABC News also reported the birth of two sets of identical twins to parents in Texas. Experts estimated the odds of this type of birth to be 1 in 70 million.