ICD-10-CM > O00-O9A > O30-O48 > O36 > O36.8 > O36.83 > O36.833 O36.833 Maternal care for abnormalities of the fetal heart rate or rhythm, third trimester Non-Billable/Non-Specific Codes O36.8330..., not applicable or unspecifiedO36.8331..., fetus 1O36.8332..., fetus 2O36.8333..., fetus 3O36.8334..., fetus 4O36.8335..., fetus 5O36.8339..., other fetus