A public service ombudsman report [the official appointed to investigate the complaint] found that the Cardiff and Vale NHS Trust and Cardiff Local Health Board (LHB) could not agree who should pay for it.
The patient, from Cardiff, arranged a private treatment and the ombudsman has recommended that she is reimbursed and compensated.
In a joint statement, the LHB and the trust both apologised to the woman.
The patient, identified only as Mrs R, requested the antenatal injection in 2006 because of her rhesus negative blood group and problems her mother had in pregnancy.
The National Institute for Clinical Excellence (Nice) recommends that the injection is offered as a routine treatment.
As well as recommending the local health board reimburse Mrs R for the cost of her treatment, ombudsman Peter Tyndall said between them the trust and the Cardiff LHB should pay her £250 for the stress.
He remained concerned the trust and LHB had still not reached an agreement over the funding of this treatment in the future.
“It is unacceptable for patients to be denied access to a treatment which they should receive on clinical grounds simply because the different NHS bodies responsible cannot agree whose budget should bear the cost.”