The first twin was born at 11:58 p.m. EST on Sunday, Dec. 31, 2017. His younger sister was born at 12:16 a.m. on January 1, 2018, at 4 pounds, 10 ounces and 16 inches long.
Rios gave birth to the twins via C-section almost 4 weeks early, she said.
The hospital wrote on Facebook that it was "honored to play a significant role in this 2018 New Year delivery of baby twins" and thanked the "dedicated" hospital staff.
The babies' parents said that they were about a month early. While siblings in such cases are usually born together, can one of them be delivered in a different year altogether?
Maria Flores was originally due to give birth on January 27, but her bundles of joy chose to make an early arrival.More news: US Resumes Visa Services in Turkey, Easing Diplomatic Strains
It appears the first baby born in Kern County was in Delano.
The miracle birth involved the pair of twins - a boy and a girl, who arrived on either side of the midnight in California's Delano Regional Medical Center.
Maria Flores' twins were born less than 20 minutes apart. "The whole family feels humbled and blessed and excited", the spokesman said.
The twins actually weren't due for another three weeks. "But then it turned out Maria was in labour, which was a surprise".
According to NBC News, a California woman rang in the New Year by giving birth in 2017 and 2018.