Prison medical staff are not obstetricians. They're usually family practitioners. And while old-time family doctors used to deliver babies, most newer grads have minimal experience because the astronomical cost of malpractice insurance for delivering one baby means they just won't ever do it. General medical issues, not childbirth.
In my experience, prisons usually have a contract with one hospital or system in the state to care for issues too complex for prison healthcare.
I'd be shocked if prisoners in the US are allowed access to doctors outside of the prison medical staff (or whoever they're outsourcing care to).