SAN JOSE -- The odds are as high as 1 in 100 million, but 24-year-old San Jose resident Yanina Rivera beat them Wednesday night at O'Connor Hospital when she gave birth to three naturally conceived identical triplet girls.

Hospital spokeswoman Donna Cumming said the first baby was born at 7:12 p.m. and weighed 4 pounds. The second arrived at 7:14 p.m., topping the scales at 4 pounds, 14 oz. The third sister followed at 7:16 p.m., weighing 4 pounds, 9 ounces. All three were delivered by Dr. Kenneth Phan, an East San Jose ob-gyn.

Experts say that naturally conceived identical triplets are extremely rare. Identical siblings are produced when an egg is divided in utero. Fraternal siblings come from different eggs.

Despite the rarity, a 42-year-old Long Beach woman in January gave birth to identical triplet boys, who were naturally conceived, instantly doubling the size of her family. And last November a 29-year-old woman in Quincy in Plumas County gave birth to identical triplet girls, also naturally conceived.

At the time, Dr. William Gilbert, director of Sutter Women's Services, told the Sacramento Bee the odds of producing identical triplets without fertility drugs was so rare it was difficult to accurately measure statistically. He placed the odds at between one in 1 million and one to 100 million.

In July 2010, 42-year-old Redwood City resident Lina Khoury gave birth to identical triplets Michael, Manawel and Marcel.

Contact Tracy Seipel at 408-920-5343. Follow her at Twitter.com/taseipel.