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O99.321 ICD-10-CM Code: Drug use complicating pregnancy, first trimester

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Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Tabular directives
1 inclusion term · 1 Excludes2 · 2 use-additional codes

Billable · FY2027A valid, specific ICD-10-CM code, reportable for dates of service in FY2027.

What you need to know

Source: CMS/NCHS Official ICD-10-CM tabular notes, quoted. From the CMS/NCHS tabular list for the release in force. A note the category or block publishes applies to this code too; the Instructions section marks which is which.

Use additional codeReport with this code when documented
  • code(s) from F11-F16 and F18-F19 to identify manifestations of the drug use
  • code to identify specific condition
Excludes2Not included here; may be reported together
  • when the reason for maternal care is that the condition is known or suspected to have affected the fetus (O35-O36)
IncludesWhat this code covers
  • conditions which complicate the pregnant state, are aggravated by the pregnancy or are a main reason for obstetric care

CompareCheck ClaimView Related Codes

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v44, Appendix B.

  • MS-DRG 817 — OTHER ANTEPARTUM DIAGNOSES WITH O.R. PROCEDURES WITH MCC (MDC 14)
  • MS-DRG 818 — OTHER ANTEPARTUM DIAGNOSES WITH O.R. PROCEDURES WITH CC (MDC 14)
  • MS-DRG 819 — OTHER ANTEPARTUM DIAGNOSES WITH O.R. PROCEDURES WITHOUT CC/MCC (MDC 14)
  • MS-DRG 831 — OTHER ANTEPARTUM DIAGNOSES WITHOUT O.R. PROCEDURES WITH MCC (MDC 14)
  • MS-DRG 832 — OTHER ANTEPARTUM DIAGNOSES WITHOUT O.R. PROCEDURES WITH CC (MDC 14)
  • MS-DRG 833 — OTHER ANTEPARTUM DIAGNOSES WITHOUT O.R. PROCEDURES WITHOUT CC/MCC (MDC 14)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for O99.321 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2027Effective: October 1, 2026

Trace:FY2027 changesChange historyRelease, file and checksum

Notes without a marker are published on O99.321 itself; “inherited from” names the category or block whose note applies here.

Includes

Conditions the official ICD-10-CM tabular list includes under this code.

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

Source: inherited from O99

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

  • when the reason for maternal care is that the condition is known or suspected to have affected the fetus (O35-O36) Compare O99.321 vs O35 →

Source: inherited from O99

Use Additional Code

Supplementary codes the tabular list directs you to add.

  • Use additional code(s) from F11-F16 and F18-F19 to identify manifestations of the drug use inherited from O99.32
  • Use additional code to identify specific condition inherited from O99

Coder workflow for O99.321

MedCoder structured workflow — derived from this code’s own official record

Before you code O99.321

  1. Confirm the condition is documented as complicating the pregnancy, childbirth, or the puerperium, and check the trimester where the code carries one and the fetus character where the category requires it. Chapter 15 codes belong on the maternal record only and take sequencing priority over codes from other chapters. It is the provider’s responsibility to state that a condition is not affecting the pregnancy; the trimester is assigned from the documentation (Guidelines I.C.15.a, I.C.15.a.1, I.C.15.a.3).

    Guide: How to choose an ICD-10-CM code →

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
Trimester
Assigned from the documented trimester at the encounter, or the trimester in which the condition developed for inpatient stays (Guidelines I.C.15.a.3).
The conditions the Use Additional Code note names
Reported with this code when documented; a conditional instruction (“if applicable”, “if known”) applies only when the record supports it.

Official instructions as workflow

  • Excludes2 — not part of O99.321(1 note)

    Coding workflow: The conditions named in this note are not included in O99.321. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

    See the official tabular notes · Guidelines I.A.12.b

  • Use Additional Code — after identifying O99.321(2 notes)

    Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with O99.321 when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

    See the official tabular notes · Guidelines I.A.13

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: A condition the Use Additional Code note names is documented.

Coding question: Is a second code reported with O99.321?

Path: Review the Use Additional Code note and the code it names.

Reason: The additional code is reported when the record documents the condition; a conditional instruction applies only when its condition is met (Guidelines I.A.13).

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Coding context

The comparisons, hierarchy, index entries, guidelines, relationships, risk-adjustment and coverage context a coder commonly needs. Each section names whether it is official source data, a MedCoder-derived relationship or MedCoder editorial.

Don’t confuse O99.321 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of O99.321 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

  • O99.320— Specificity relationship (Review)

    Overlapping diagnoses in the same category.

    Overlapping codes in the same category — the documentation decides which is the more specific fit.

    What moves you there: A record that documents no more than “Drug use complicating pregnancy, unspecified trimester” takes O99.320; specificity in the record moves it back here.

    Full comparison: O99.321 vs O99.320 →

  • O35— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of when the reason for maternal care is that the condition is known or suspected to have affected the fetus adds O35; it is not part of this code and both may be reported when both are documented.

    Full comparison: O99.321 vs O35 →

  • O36— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of when the reason for maternal care is that the condition is known or suspected to have affected the fetus adds O36; it is not part of this code and both may be reported when both are documented.

    Full comparison: O99.321 vs O36 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Code Overview

Drug use complicating pregnancy, first trimester is a billable ICD-10-CM diagnosis code (O99.321).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Official Coding Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Verbatim excerpts from the ICD-10-CM Official Guidelines for Coding and Reporting (CMS/NCHS) that govern this code.

Chapter 15: Pregnancy, Childbirth, and the Puerperium (O00-O9A)

3) Drug use during pregnancy, childbirth and the puerperium Codes under subcategory O99.32, Drug use complicating pregnancy, childbirth, and the puerperium, should be assigned for any pregnancy case when a patient uses drugs during the pregnancy or postpartum. This can involve illegal drugs, or inappropriate use or abuse of prescription drugs. Secondary code(s) from categories F11-F16 and F18-F19 should also be assigned to identify manifestations of the drug use.

Verify Before Coding

  • Age-restricted: the Medicare Code Editor lists this as a maternity (age 9-64) diagnosis; other ages are presumed incorrect.
  • CC as a secondary diagnosis (FY2027). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder-derived relationships — computed from published CMS and AHRQ datasets

Other codes that name O99.321 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 11 Excludes2 notes across 2 chapters: O20 — Hemorrhage in early pregnancy (via O99.-), O20-O29 — Other maternal disorders predominantly related to pregnancy (O20-O29) (via O99.-), O21 — Excessive vomiting in pregnancy (via O99.-), O22 — Venous complications and hemorrhoids in pregnancy (via O99.-), O23 — Infections of genitourinary tract in pregnancy (via O99.-), O24 — Diabetes mellitus in pregnancy, childbirth, and the puerperium (via O99.-), O25 — Malnutrition in pregnancy, childbirth and the puerperium (via O99.-), O26 — Maternal care for other conditions predominantly related to pregnancy (via O99.-), O28 — Abnormal findings on antenatal screening of mother (via O99.-), O29 — Complications of anesthesia during pregnancy (via O99.-), Z79 — Long term (current) drug therapy (via O99.32.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

MS-DRG Grouper Relationships (FY2027)

Potential MS-DRG participation — not a DRG assignment.

FY2027 MS-DRG: CC — Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 226 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 6 MS-DRGs: DRG 817 (MDC 14), DRG 818 (MDC 14), DRG 819 (MDC 14), DRG 831 (MDC 14), DRG 832 (MDC 14), DRG 833 (MDC 14).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):PRG028 — Other specified complications in pregnancy (default); MBD025 — Other specified substance-related disorders.

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as CC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

O99.213 — Obesity complicating pregnancy, third trimester, O99.214 — Obesity complicating childbirth, O99.215 — Obesity complicating the puerperium, O99.280 — Endocrine, nutritional and metabolic diseases complicating pregnancy, unspecified trimester, O99.281 — Endocrine, nutritional and metabolic diseases complicating pregnancy, first trimester, O99.282 — Endocrine, nutritional and metabolic diseases complicating pregnancy, second trimester, O99.283 — Endocrine, nutritional and metabolic diseases complicating pregnancy, third trimester, O99.284 — Endocrine, nutritional and metabolic diseases complicating childbirth, O99.285 — Endocrine, nutritional and metabolic diseases complicating the puerperium, O99.320 — Drug use complicating pregnancy, unspecified trimester, 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, O99.330 — Smoking (tobacco) complicating pregnancy, unspecified trimester, O99.331 — Smoking (tobacco) complicating pregnancy, first trimester, O99.332 — Smoking (tobacco) complicating pregnancy, second trimester, O99.333 — Smoking (tobacco) complicating pregnancy, third trimester, O99.334 — Smoking (tobacco) complicating childbirth, O99.335 — Smoking (tobacco) complicating the puerperium, +205 more

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical categories (Other specified complications in pregnancy, Other specified substance-related disorders).

F19.959 — Other psychoactive substance use, unspecified with psychoactive substance-induced psychotic disorder, unspecified, F19.96 — Other psychoactive substance use, unspecified with psychoactive substance-induced persisting amnestic disorder, F19.97 — Other psychoactive substance use, unspecified with psychoactive substance-induced persisting dementia, F19.980 — Other psychoactive substance use, unspecified with psychoactive substance-induced anxiety disorder, F19.981 — Other psychoactive substance use, unspecified with psychoactive substance-induced sexual dysfunction, F19.982 — Other psychoactive substance use, unspecified with psychoactive substance-induced sleep disorder, F19.988 — Other psychoactive substance use, unspecified with other psychoactive substance-induced disorder, F19.99 — Other psychoactive substance use, unspecified with unspecified psychoactive substance-induced disorder, O35.5XX0 — Maternal care for (suspected) damage to fetus by drugs, not applicable or unspecified, O35.5XX1 — Maternal care for (suspected) damage to fetus by drugs, fetus 1, O35.5XX2 — Maternal care for (suspected) damage to fetus by drugs, fetus 2, O35.5XX3 — Maternal care for (suspected) damage to fetus by drugs, fetus 3, O35.5XX4 — Maternal care for (suspected) damage to fetus by drugs, fetus 4, O35.5XX5 — Maternal care for (suspected) damage to fetus by drugs, fetus 5, O35.5XX9 — Maternal care for (suspected) damage to fetus by drugs, other fetus, O99.320 — Drug use complicating pregnancy, unspecified trimester, 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, +367 more

Contextual Map

Every relationship of O99.321 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run O99.321 with these 8 related codes in Claim Check

Hierarchy

Referenced by Excludes2 notes (11)

Clinical classification (CCSR)

MS-DRG Grouper

MDC crossing

  • MDC 14 — Pregnancy, Childbirth and the Puerperium[MDC crossing]: “Pregnancy, Childbirth and the Puerperium — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 94 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2027

Nearest codes (40)

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Deep reference

Published questions and FAQ, every source behind this page with its release and checksum, the date-of-service check and the complete change history.

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2027 tabular list, index and tables, effective October 1, 2026 Release, file and checksum · Publisher’s page
Coding guidelines Official source data
ICD-10-CM Official Guidelines for Coding and Reporting (FY2027), quoted by section Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v44.0 (October 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v44 Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder-derived relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder editorial explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Current data releases:ICD-10-CM FY2027 · ICD-10-PCS FY2027 · HCPCS October 2026 · MS-DRG v44 · Medicare Code Editor v44.0 · NCCI PTP Q4 2026 · MUE Q4 2026 · NCD code lists 2026-01 · LCD export September 20, 2026 · All releases and sources

Labels on this page: Official source data · MedCoder-derived relationship · MedCoder editorial explanation. How to read the labels · All data sources and release dates · CMS coding rules

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "O99.321 — Drug use complicating pregnancy, first trimester." ICD-10-CM FY2027. https://medcoder.ai/icd10/code/o99.321-drug-use-complicating-pregnancy-first-trimester

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Drug use complicating pregnancy, first trimester

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027, and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to O99.321 in its code family, with their registry titles.

View all codes in the O99 family