2026 ICD-10-CM Diagnosis Code O11.9Pre-existing hypertension with pre-eclampsia, unspecified trimester

ICD-10-CM Codes›O00-O9A›O10-O16›O11

ICD-10-CM O11.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

O11.9 is a billable ICD-10-CM diagnosis code for pre-existing hypertension with pre-eclampsia, unspecified trimester. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 817 through 819, 831 through 833. The code is restricted by the Medicare Code Editor to maternity cases (age 9 through 64). Coders also document this condition as pre-eclampsia. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Hypertension and hypertensive-related conditions complicating pregnancy; childbirth; and the puerperium and Hypertension with complications and secondary hypertension.

Code Identity

ICD-10-CM Code
O11.9
Billable Status
Yes — Valid for Submission
Code Describes
Pre-existing hypertension with pre-eclampsia, unspecified trimester
Short Description
Pre-existing hypertension with pre-eclampsia, unsp trimester
Parent Code
O11
Pre-existing hypertension with pre-eclampsia

Code Classification

ChapterO00-O9APregnancy, childbirth and the puerperium
SectionO10-O16Edema, proteinuria and hypertensive disorders in pregnancy, childbirth and the puerperium
CategoryO11Pre-existing hypertension with pre-eclampsia
This CodeO11.9Pre-existing hypertension with pre-eclampsia, unspecified trimester

Code EditsBilling

Medicare Code Editor checks that affect claim validity for O11.9.

Maternity diagnoses
The Medicare Code Editor detects inconsistencies in maternity cases by checking a patient's age and any diagnosis on the patient's record. The maternity code edits apply to patients age ange is 9–64 years inclusive (e.g., diabetes in pregnancy, antepartum pulmonary complication).

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Pre-eclampsia
  • Pre-eclampsia added to pre-existing hypertension
  • Pre-eclampsia or eclampsia with pre-existing hypertension

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR PRG020
Hypertension and hypertensive-related conditions complicating pregnancy; childbirth; and the puerperium
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR CIR008
Hypertension with complications and secondary hypertension
Default principal diagnosis: inpatient No · outpatient No

Patient EducationClinical

High Blood Pressure in Pregnancy

Blood pressure is the force of your blood pushing against the walls of your arteries. Your arteries are blood vessels that carry blood from your heart to other parts of your body. High blood pressure, or hypertension, is blood pressure that is higher than normal.

The full article covers:

  • What is high blood pressure in pregnancy?
  • What are the types of high blood pressure in pregnancy?
  • Who is more likely to develop high blood pressure in pregnancy?
  • What are the symptoms of high blood pressure in pregnancy?
  • What problems can high blood pressure in pregnancy cause?
  • How is high blood pressure in pregnancy diagnosed?
  • What are the treatments for high blood pressure in pregnancy?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert O11.9 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
642.20 Old hyperten preg-unspec
Approximate The match is approximate rather than exact.
ICD-9-CM
642.70 Tox w old hyperten-unsp
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About O11.9Overview

Is O11.9 (Pre-existing hypertension with pre-eclampsia) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report pre-existing hypertension with pre-eclampsia, unspecified trimester on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does O11.9 group to?

When pre-existing hypertension with pre-eclampsia, unspecified trimester is the principal diagnosis on an inpatient stay, it groups to MS-DRG 817, 818, 819, 831, 832, 833, with relative weights from 0.5229 to 1.6880 depending on complications. Higher weights mean higher Medicare reimbursement.

Who can O11.9 be reported for?

The Medicare Code Editor checks pre-existing hypertension with pre-eclampsia, unspecified trimester against patient demographics: this code is intended for maternity cases (age 9 through 64). Claims outside these limits are flagged as inconsistent.

What is the ICD-9 equivalent of O11.9?

Under the General Equivalence Mappings, pre-existing hypertension with pre-eclampsia, unspecified trimester converts to ICD-9-CM 642.20 (old hyperten preg-unspec) and 642.70 (tox w old hyperten-unsp). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.