Surgeons performed the world's first in-utero surgery on a 17-week old fetus, after an ultrasound scan revealed that the unborn baby had a rare and fatal tumor growing from its mouth.

Doctors said that the only way to save the unborn infant now known as Leyna Gonzalez was to remove the peach-size tumor from her mouth while she was still in the womb, a procedure that has never been performed.

In a breakthrough operation, doctors at Jackson Memorial Hospital performed the surgery on Leyna's mother, Tammy Gonzales, while she was still awake and carefully detached Leyna's oral tumor with a laser.

"I could see it floating down", the 39-year old mother told a press conference on Thursday. "It was like this huge weight had been lifted off. It just floated away and I could finally see her face."

The operation was performed in 2010, the story has only just been made public because experts had to wait for their report to be published in a scientific journal American Journal of Obstetrics & Gynaecology.

Leyna had a fetal oral teratoma, a rare condition that affects less than one in 100,000 pregnancies. Doctors had told Tammy to consider abortion because there was a very slim chance that her daughter would survive birth, and if she did she would need an immediate tracheotomy to breathe and to endure many more future surgeries.

Desperate to save their unborn daughter, Tammy and her husband Alain went to Dr. Ruben Quintero, a pioneer in fetal medicine at the University of Miami who has treated many high-risk conditions in babies still in the womb.

"The concern with these tumors is they can grow very rapidly," Dr. Quintero said at the press conference. "They can cause bleeding, which can cause the death of the baby."

Doctors had warned that the rapidly growing tumor could have eventually weighed as much as two pounds and result in fatal bleeding.

The surgery was performed by both Dr. Quintero and Dr. Efitichia Kontopoulos in May 2010.

Doctors had used an endoscope guided by ultrasound to cut the tumor from the then 20-week old baby's mouth. Tammy had remained awake and was only given local anesthesia for the procedure which lasted for about an hour.

Five months after the operation, Leyna was born with no problems and weighed 8lbs 1oz, and the only trace of her tumor ever being there is a small surgical scar on her mouth.

"This is an opportunity to expand the field that we have developed, with this ability to treat birth defects in utero, and give hope to mothers," Dr. Quintero said.

"They are her saviors," Tammy said about the doctors who performed the surgery to save Leyna. "She wouldn't be here without them."