O16.1 Unspecified maternal hypertension, first trimester

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis.

MS-DRG index

Defines the logic of DRG(s) 817-819 in MDC 14.

Approximate ICD-9-CM (GEMs)

• 642.91 Unspecified hypertension complicating pregnancy, childbirth, or the puerperium, delivered, with or without mention of antepartum condition (approximate)
• 642.93 Unspecified hypertension complicating pregnancy, childbirth, or the puerperium, antepartum condition or complication (approximate)
• 642.94 Unspecified hypertension complicating pregnancy, childbirth, or the puerperium, postpartum condition or complication (approximate)

Medicare Code Edits (MCE v43.1 (April 2026))

• Maternity diagnoses (age 9 through 64): Age conflict edit. These diagnoses are clinically expected only in patients age 9 through 64.

Code annotations containing back-references to O16.1

Back-references to O16

• Type 1 Excludes: I10 Essential (primary) hypertension ("hypertensive disease complicating pregnancy, childbirth and the puerperium (O10-O11, O13-O16)")
• Type 2 Excludes: O99.4 Diseases of the circulatory system complicating pregnancy, childbirth and the puerperium ("hypertensive disorders (O10-O16)")

Nearby codes

• O16 Unspecified maternal hypertension
• O16.1 Unspecified maternal hypertension, first trimester (this code)
• O16.2 Unspecified maternal hypertension, second trimester
• O16.3 Unspecified maternal hypertension, third trimester
• O16.4 Unspecified maternal hypertension, complicating childbirth
• O16.5 Unspecified maternal hypertension, complicating the puerperium
• O16.9 Unspecified maternal hypertension, unspecified trimester