2026 ICD-10-CM Diagnosis Code O26.40Herpes gestationis, unspecified trimester

ICD-10-CM Codes›O00-O9A›O20-O29›O26

ICD-10-CM O26.40
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

O26.40 is a billable ICD-10-CM diagnosis code for herpes gestationis, 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 herpes gestationis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified complications in pregnancy and Viral infection.

This medical diagnosis code is frequently used in OB/GYN medical specialties to designate conditions such maternal disorders related to pregnancy.

Code Identity

ICD-10-CM Code
O26.40
Billable Status
Yes — Valid for Submission
Code Describes
Herpes gestationis, unspecified trimester
Short Description
Herpes gestationis, unspecified trimester
Same as the full description in the CMS dataset.
Parent Code
O26.4
Herpes gestationis

Code Classification

ChapterO00-O9APregnancy, childbirth and the puerperium
SectionO20-O29Other maternal disorders predominantly related to pregnancy
CategoryO26Maternal care for other conditions predominantly related to pregnancy
This CodeO26.40Herpes gestationis, unspecified trimester

Code EditsBilling

Medicare Code Editor checks that affect claim validity for O26.40.

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.

  • Herpes gestationis

Clinical ClassificationClinical

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

CCSR PRG028
Other specified complications in pregnancy
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INF008
Viral infection
Default principal diagnosis: inpatient No · outpatient No

Patient EducationClinical

Health Problems in Pregnancy

A health problem in pregnancy is any disease or condition that could affect your health or the health of your fetus. Some health problems may make it more likely that you will have a high-risk pregnancy. A high-risk pregnancy is one in which you, your fetus, or both are at higher risk for health problems than in a typical pregnancy.

The full article covers:

  • What are health problems in pregnancy?
  • What raises my risk for health problems during pregnancy?
  • Can chronic health conditions cause problems in pregnancy?
  • Can health problems in pregnancy be prevented?

Read the full article at MedlinePlus

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

Convert O26.40 to ICD-9-CMHistory

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

ICD-9-CM
646.80 Preg compl NEC-unspec
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 O26.40Overview

Is O26.40 (Herpes gestationis) a billable code?

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

What MS-DRG does O26.40 group to?

When herpes gestationis, 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 O26.40 be reported for?

The Medicare Code Editor checks herpes gestationis, 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 O26.40?

Under the General Equivalence Mappings, herpes gestationis, unspecified trimester converts to ICD-9-CM 646.80 (preg compl NEC-unspec). 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.