Well, I'm no constitutional scholar, but it seems to me the 14th amendment defined federal citizens, but never removed the definition of state citizen.
14th Amendment. "Section 1. All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws."
How would the federal government circumvent a state giving the rights of citizenship to the unborn?
Because the federal government has already declared the unborn nonpersons—state law cannot overturn federal law.