The twins' mother, Maria Esperanza Flores Rios, had a due date of January 27 but was scheduled for a C-section January 10 due to her high-risk pregnancy.
The Delano's Hospital said Joaquin was the county's last baby of 2017 and Aitana was the first of 2018.
The unlikely event of a birth like this also gifted their parents the chance to take home more than $3,000 worth of baby supplies that were donated to the hospital by local community groups.
Although the brother and sister might not have exactly the same birth date, we're that spending about 9 months in the womb together trumps the few minutes they spent apart. While siblings in such cases are usually born together, can one of them be delivered in a different year altogether?More news: Manchester City reveal Gabriel Jesus has suffered MCL injury
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Joaquin and Aitana de Jesus Ontiveros were both due to arrive January 27, 2018.
New Year's births make good press, especially when they are this unusual. "The whole family feels humbled and blessed and excited", the spokesman said.
Southern California resident Maria Esperanza Flores Rio, 39, gave birth to New Year's twins in two different years.
Identical twins are known to be born at a rate of nearly four per 1000 births across the globe but few of these births turn out to be special.