The implementation guide specifications for the 271 do not currently allow return of the subscriber date of birth (DOB) if the subscriber is not the patient.  Specifically, the DMG segment includes notes as follows: 1. “Use this segment to convey the birth date or gender demographic information for the subscriber”, 2. “Use this segment only if the subscriber is the patient….” 

Hospitals need this subscriber data for several reasons including to determine coordination of benefits.  The rule for children covered under both parents insurance is that the plan of the parent whose birthday falls earliest in the year is primary.  If there is no information on the parents date of birth, the hospital cannot make a determination as to which plan is primary.