(CNN) -- Kimberly and Craig Fugate were expecting Kenleigh, Kristen and Kayleigh. But Kelsey, born with her sisters on February 8, was a complete surprise.
The identical quadruplets were born via cesarean section in the Winfred L. Wiser Hospital for Women and Infants at the University of Mississippi Medical Center in Jackson, Mississippi.
"They had gotten the three out and they said, 'More feet,'" the mother told CNN affiliate WAPT. "I said, 'No!' It was an instant shock."
The odds of spontaneous quadruplets -- conceived without fertility assistance -- are 1 in 729,000, according to Dr. James Bofill, Kimberly Fugate's physician and a professor of maternal fetal medicine at the University of Mississippi.
The odds in this case were even slimmer as the Fugate girls are identical, meaning they split from a single egg.
"Those odds are incalculable," Bofill said in a hospital press release.
The last known set of identical quadruplets was born in Germany in January 2012. Experts estimate there are 50 to 60 sets worldwide.
You may know the Mathias quads -- Grace, Emily, Mary Claire and Anna -- who are in the eighth grade and appeared on the Discovery Health Channel's "Super Quads." And perhaps you remember a Lifetime reality show called "Four of a Kind," which featured identical quadruplets Megan, Kendra, Sarah and Calli Durst, of Buffalo, Minnesota.
The Fugates were originally surprised to learn they were pregnant at all, according to WAPT. Then in November, the 42-year-old mom was told she was having triplets. The fourth baby managed to keep her existence a secret until Fugate went into labor at 28 weeks.
Kenleigh Rosa was born at 7:55, weighing 2 pounds, 1 ounce.
Kristen Sue was born at 7:57 weighing 2 pounds, 4 ounces.
Kayleigh Pearl was born at 7:58 weighing 2 pounds, 8 ounces.
And Kelsey Roxanne was born a minute later weighing 2 pounds, 6 ounces.
Bofill told The Clarion Ledger the hidden quad was a first in his 27-year career.
"I was very embarrassed, obviously," Bofill said. "The news was sent to me by one of my fellows. I thought she was kidding."
The quadruplets join older sister Katelyn, who is 10 years old. It's unclear when they'll be able to go home.
"Typically, when babies are born prematurely, doctors tell the families to expect them to stay in the (neonatal intensive care unit) until their original due date, which in this case would be May 2," said hospital spokeswoman Jennifer Hospodor. "It is possible that some or all of the girls would be stronger enough to go home before that, or have to stay longer. It depends on how they develop over the next 12 weeks."