O99.343 Other mental disorders complicating pregnancy, third trimester

Billable ICD-10-CM code, FY2026.

Applies from O99 Other maternal diseases classifiable elsewhere but complicating pregnancy, childbirth and the puerperium

Includes

• conditions which complicate the pregnant state, are aggravated by the pregnancy or are a main reason for obstetric care

Excludes2 (not included here)

• when the reason for maternal care is that the condition is known or suspected to have affected the fetus (O35-O36)

Use additional code

• code to identify specific condition

Applies from O99.34 Other mental disorders complicating pregnancy, childbirth, and the puerperium

Applicable to

• Conditions in F01-F09, F20-F52 and F54-F99

Excludes2 (not included here)

• postpartum mood disturbance (O90.6)
• postnatal psychosis (F53.1)
• puerperal psychosis (F53.1)

MS-DRG index

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

Approximate ICD-9-CM (GEMs)

• 648.41 Mental disorders of mother, delivered, with or without mention of antepartum condition (approximate)
• 648.43 Mental disorders of mother, antepartum condition or complication (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.

Nearby codes

• O99.335 Smoking (tobacco) complicating the puerperium
• O99.34 Other mental disorders complicating pregnancy, childbirth, and the puerperium
• O99.340 Other mental disorders complicating pregnancy, unspecified trimester
• O99.341 Other mental disorders complicating pregnancy, first trimester
• O99.342 Other mental disorders complicating pregnancy, second trimester
• O99.343 Other mental disorders complicating pregnancy, third trimester (this code)
• O99.344 Other mental disorders complicating childbirth
• O99.345 Other mental disorders complicating the puerperium
• O99.35 Diseases of the nervous system complicating pregnancy, childbirth, and the puerperium
• O99.350 Diseases of the nervous system complicating pregnancy, unspecified trimester
• O99.351 Diseases of the nervous system complicating pregnancy, first trimester