O66.40 ICD-10-CM Code: Failed trial of labor, unspecified
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FY 2026 Apr update / Pregnancy, childbirth and the puerperium (O00-O9A) / Complications of labor and delivery (O60-O77)
O66.40
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceFailed trial of labor, unspecified
A trial of labor that did not result in vaginal delivery, requiring cesarean section, without specification of the exact reason for failure.
CMS-HCC V28
N/A—
Not mapped
CMS-HCC V24
N/A—
Not mapped
ACA/HHS
MappedHCC 208
Varies by metal level
ESRD/PACE
N/A—
Not mapped
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for O66.40 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for O66.40 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for O66.40 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for O66.40 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for O66.40 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for O66.40 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for O66.40 in this effective period.
Buddy Documentation Tip
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is O66.40 an HCC code?
No. O66.40 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
- Code
- O66.40
- Description
- Failed trial of labor, unspecified
- HCC (V28)
- No CMS-HCC V28 mapping
- RAF
- —
- Billable
- Yes
- Payment year
- 2026
Coder workflow notes
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This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
O66.40 is the ICD-10-CM diagnosis code for failed trial of labor, unspecified. A trial of labor that did not result in vaginal delivery, requiring cesarean section, without specification of the exact reason for failure. O66.40 sits in the ICD-10-CM chapter for pregnancy, childbirth and the puerperium (o00-o9a), within the section covering complications of labor and delivery (o60-o77).
O66.40 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
Use this code when documentation indicates a failed trial of labor (TOLAC) but does not specify whether it was due to failed VBAC or other causes.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for O66.40 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code when documentation indicates a failed trial of labor (TOLAC) but does not specify whether it was due to failed VBAC or other causes
- •Review operative reports and labor notes to determine if a more specific code (O66.41) should be used instead