SAN DIEGO -- Physicians at UC San Diego Medical Center performed the first in-utero surgery in Southern California to save the life of two unborn twin boys, hospital officials announced Thursday.

The procedure, known as fetoscopy, was performed at 20 weeks gestation to correct a deadly condition known as twin-to-twin transfusion syndrome, where one twin was receiving too much blood and the other not enough.

"So one baby ends up with the lion's share, while the other becomes quite anemic from lack of blood," the surgeon, Dr. David Schrimmer told local media.

The babies' mother, Millie Tinoisamoa, called the surgery a "miracle."

"It's amazing that the surgery went fine and everything went successfully," Tinoisamoa told reporters.

Without the intervention, UCSD Medical Center officials said the twins would not have survived the pregnancy.

The babies were born prematurely at 29 weeks on Sept. 12 and are being cared for at the UCSD Infant Special Care Center in Hillcrest.

UCSD is the first medical center in Southern California to employ fetoscopy to save the lives of fetuses with life-threatening conditions, hospital officials said.

Guided by ultrasound, physicians used a laser, or photocoagulation, to close the blood vessels on the surface of the placenta so that the babies no longer share blood vessels.

The procedure takes about two hours.