This should only be an issue if the patient does not have coverage during the time span you have listed on the claim. Check the policy of the insurer that is denying the claim for timely filing and be sure it does not state 30 days or less. There should be no timely filing limit for ob services and this can be discussed with the insurer. Be sure to appeal every denial and get your providers involved if they have signed a contract with a short timely filing clause for ob services. They are certainly not applying to the delivery global code so there is no reason it should be applied to ob antepartum services.