O16Unspecified maternal hypertension

O16 is the ICD-10-CM diagnosis code for unspecified maternal hypertension. It belongs to block O10-O16 (edema, proteinuria and hypertensive disorders in pregnancy, childbirth and the puerperium) and chapter 15 (pregnancy, childbirth and the puerperium). It is a header code, so it can't be reported by itself; one of its 6 subcodes must be used instead.

To report this condition, pick the subcode that matches the documentation: O16.1 (first trimester), O16.2 (second trimester), O16.3 (third trimester), O16.4 (complicating childbirth), O16.5 (complicating the puerperium) and O16.9 (unspecified trimester).

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.