O66.1 Obstructed labor due to locked twins

Billable ICD-10-CM code, FY2026.

MS-DRG index

Defines the logic of DRG(s) 817-819 in MDC 14.

Approximate ICD-9-CM (GEMs)

• 660.51 Locked twins, delivered, with or without mention of antepartum condition (approximate)

Medicare Code Edits (MCE v43.1 (April 2026))

• Maternity diagnoses (age 9 through 64): Age conflict edit. These diagnoses are clinically expected only in patients age 9 through 64.

Code annotations containing back-references to O66.1

Back-references to O66

• Type 1 Excludes: O33 Maternal care for disproportion ("disproportion with obstructed labor (O65-O66)")

Diagnosis Index entries for O66.1

• Delivery (childbirth) (labor) › complicated › by › obstructed labor › due to › locked twins
• Locked twins causing obstructed labor

Nearby codes

• O66 Other obstructed labor
• O66.0 Obstructed labor due to shoulder dystocia
• O66.1 Obstructed labor due to locked twins (this code)
• O66.2 Obstructed labor due to unusually large fetus
• O66.3 Obstructed labor due to other abnormalities of fetus
• O66.4 Failed trial of labor
• O66.40 Failed trial of labor, unspecified
• O66.41 Failed attempted vaginal birth after previous cesarean delivery