2026 ICD-10-CM Diagnosis Code O91.212Nonpurulent mastitis associated with pregnancy, second trimester

ICD-10-CM Codes›O00-O9A›O85-O92›O91

ICD-10-CM O91.212
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

O91.212 is a billable ICD-10-CM diagnosis code for nonpurulent mastitis associated with pregnancy, second 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). In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Nonmalignant breast conditions and Other specified complications in pregnancy.

Code Identity

ICD-10-CM Code
O91.212
Billable Status
Yes — Valid for Submission
Code Describes
Nonpurulent mastitis associated with pregnancy, second trimester
Short Description
Nonpurulent mastitis assoc w pregnancy, second trimester
Parent Code
O91.21
Nonpurulent mastitis associated with pregnancy

Code Classification

ChapterO00-O9APregnancy, childbirth and the puerperium
SectionO85-O92Complications predominantly related to the puerperium
CategoryO91Infections of breast associated with pregnancy, the puerperium and lactation
This CodeO91.212Nonpurulent mastitis associated with pregnancy, second trimester

Code EditsBilling

Medicare Code Editor checks that affect claim validity for O91.212.

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).

Clinical ClassificationClinical

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

CCSR GEN017
Nonmalignant breast conditions
Default principal diagnosis: inpatient No · outpatient No
CCSR PRG028
Other specified complications in pregnancy
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Breast Diseases

Breast diseases include various conditions and changes in your breast. Most women experience breast changes at some time. Your age, hormone levels, and medicines you take may cause lumps, bumps, and discharges of fluids that are not breast milk.

The full article covers:

  • What are breast diseases?
  • What are the symptoms of breast disease?
  • How are breast diseases diagnosed?
  • What are the treatments for breast disease?

Read the full article at MedlinePlus

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

Convert O91.212 to ICD-9-CMHistory

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

ICD-9-CM
675.21 Mastitis-delivered
Approximate The match is approximate rather than exact.
ICD-9-CM
675.23 Mastitis-antepartum
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 O91.212Overview

Is O91.212 (Nonpurulent mastitis associated with pregnancy) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report nonpurulent mastitis associated with pregnancy, second trimester on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does O91.212 group to?

When nonpurulent mastitis associated with pregnancy, second 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 O91.212 be reported for?

The Medicare Code Editor checks nonpurulent mastitis associated with pregnancy, second 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 O91.212?

Under the General Equivalence Mappings, nonpurulent mastitis associated with pregnancy, second trimester converts to ICD-9-CM 675.21 (mastitis-delivered) and 675.23 (mastitis-antepartum). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.