Question: Can I bill two or more units for a fetal non-stress test (NST) during one session for a multiple-gestation patient? Arkansas Subscriber Answer: Yes, you can separately report each test (59025, Fetal non-stress test). Instead of using the units field on the CMS 1500 form, however, you might want to append modifier -59 (Distinct procedural service) on the second and subsequent tests to show the payer that each is a different "patient" encounter. In this case, the patient is the fetus. When you report the multiple NSTs, be sure to include a "twin" diagnosis -- such as 651.03 (Twin pregnancy; antepartum condition or complication) -- in addition to the reason the physician performed the test.