Poisoning, toxic effects, adverse effects and underdosing in a pregnant patient

A code from subcategory O9A.2, Injury, poisoning and certain other consequences of external causes complicating pregnancy, childbirth, and the puerperium, should be sequenced first, followed by the appropriate injury, poisoning, toxic effect, adverse effect or underdosing code, and then the additional code(s) that specifies the condition caused by the poisoning, toxic effect, adverse effect or underdosing.

See Section I.C.19. Adverse effects, poisoning, underdosing and toxic effects.