2026 ICD-10-CM Diagnosis Code O66.40Failed trial of labor, unspecified

ICD-10-CM Codes›O00-O9A›O60-O77›O66

ICD-10-CM O66.40
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

O66.40 is a billable ICD-10-CM diagnosis code for failed trial of labor, unspecified. 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 failed trial of labor. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Malposition, disproportion or other labor complications.

Code Identity

ICD-10-CM Code
O66.40
Billable Status
Yes — Valid for Submission
Code Describes
Failed trial of labor, unspecified
Short Description
Failed trial of labor, unspecified
Same as the full description in the CMS dataset.
Parent Code
O66.4
Failed trial of labor

Code Classification

ChapterO00-O9APregnancy, childbirth and the puerperium
SectionO60-O77Complications of labor and delivery
CategoryO66Other obstructed labor
This CodeO66.40Failed trial of labor, unspecified

Code EditsBilling

Medicare Code Editor checks that affect claim validity for O66.40.

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.

  • Failed trial of labor

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Delivery(childbirth) (labor)
      • cesarean (for)
        • failed
          • trial of labor NOS
    • Delivery(childbirth) (labor)
      • complicated
        • by
          • failed
            • trial of labor
    • Failure, failed
      • trial of labor (with subsequent cesarean delivery)

Clinical ClassificationClinical

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

CCSR PRG024
Malposition, disproportion or other labor complications
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Childbirth Problems

Childbirth is the process of giving birth to a baby. It includes labor and delivery. Usually everything goes well, but problems can happen. They may cause a risk to the mother, baby, or both. Some of the more common childbirth problems include:

Read the full article at MedlinePlus

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

Convert O66.40 to ICD-9-CMHistory

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

ICD-9-CM
660.61 Fail trial lab NOS-deliv
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 O66.40Overview

Is O66.40 (Failed trial of labor) a billable code?

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

What MS-DRG does O66.40 group to?

When failed trial of labor, unspecified 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 O66.40 be reported for?

The Medicare Code Editor checks failed trial of labor, unspecified 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 O66.40?

Under the General Equivalence Mappings, failed trial of labor, unspecified converts to ICD-9-CM 660.61 (fail trial lab NOS-deliv). 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.