O99.321 Drug use complicating pregnancy, first trimester

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis.

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 O99.32 Drug use complicating pregnancy, childbirth, and the puerperium

Use additional code

• code(s) from F11-F16 and F18-F19 to identify manifestations of the drug use

MS-DRG index

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

Approximate ICD-9-CM (GEMs)

• 648.31 Drug dependence of mother, delivered, with or without mention of antepartum condition (approximate)
• 648.33 Drug dependence 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.

Code annotations containing back-references to O99.321

Back-references to O99.32

• Type 2 Excludes: Z79 Long term (current) drug therapy ("drug use complicating pregnancy, childbirth, and the puerperium (O99.32-)")

Nearby codes

• O99.313 Alcohol use complicating pregnancy, third trimester
• O99.314 Alcohol use complicating childbirth
• O99.315 Alcohol use complicating the puerperium
• O99.32 Drug use complicating pregnancy, childbirth, and the puerperium
• O99.320 Drug use complicating pregnancy, unspecified trimester
• O99.321 Drug use complicating pregnancy, first trimester (this code)
• O99.322 Drug use complicating pregnancy, second trimester
• O99.323 Drug use complicating pregnancy, third trimester
• O99.324 Drug use complicating childbirth
• O99.325 Drug use complicating the puerperium
• O99.33 Tobacco use disorder complicating pregnancy, childbirth, and the puerperium