Q89.4 ICD-10-CM Code: Conjoined twins

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for Q89.4 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Indexed Clinical Terms (18)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

• Conjoined twins
• Craniopagus
• Dicephalus, dicephaly
• Double, monster
• Epignathus
• Fusion, fused (congenital), twins
• Ischiopagus
• Janiceps
• Monster, monstrosity (single), twin
• Parasitic, twin
• Pygopagus
• Rudimentary (congenital), respiratory organs in thoracopagus
• Siamese twin
• Sternopagus
• Syncephalus
• Thoracopagus
• Twin (newborn), conjoined
• Xiphopagus

Don’t confuse Q89.4 with…

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

The codes most likely to be picked instead of Q89.4 — 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.

• Q89.9— 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 “Congenital malformation, unspecified” takes Q89.9; specificity in the record moves it back here.

  Full comparison: Q89.4 vs Q89.9 →

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.

Verify Before Coding

• MCC as a secondary diagnosis (FY2026). 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 structured relationships — computed from published CMS and AHRQ datasets

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: MCC — Major 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 3 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 5 MS-DRGs: DRG 393 (MDC 06), DRG 394 (MDC 06), DRG 395 (MDC 06), DRG 791 (MDC 15), DRG 793 (MDC 15).

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

Clinical classification (AHRQ CCSR):MAL010 — Other specified and unspecified congenital anomalies (default).

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 MCC — 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.

Q89.7 — Multiple congenital malformations, not elsewhere classified, Q89.9 — Congenital malformation, unspecified

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Other specified and unspecified congenital anomalies).

Q87.43 — Marfan syndrome with skeletal manifestation, Q87.5 — Other congenital malformation syndromes with other skeletal changes, Q87.81 — Alport syndrome, Q87.82 — Arterial tortuosity syndrome, Q87.83 — Bardet-Biedl syndrome, Q87.84 — Laurence-Moon syndrome, Q87.85 — MED13L syndrome, Q87.87 — Hao-Fountain Syndrome, Q87.88 — CTNNB1 syndrome, Q87.89 — Other specified congenital malformation syndromes, not elsewhere classified, Q89.01 — Asplenia (congenital), Q89.09 — Congenital malformations of spleen, Q89.1 — Congenital malformations of adrenal gland, Q89.2 — Congenital malformations of other endocrine glands, Q89.3 — Situs inversus, Q89.7 — Multiple congenital malformations, not elsewhere classified, Q89.8 — Other specified congenital malformations, Q89.81 — Kabuki syndrome, Q89.89 — Other specified congenital malformations, Q89.9 — Congenital malformation, unspecified, +59 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Fusion, fused”, “Rudimentary”, “Double”; these codes share that main term but sit in a different category of the Tabular List.

Q52.79 — Other congenital malformations of vulva (vulva), Q55.1 — Hypoplasia of testis and scrotum (testes), Q56.1 — Male pseudohermaphroditism, not elsewhere classified (uterus, in male), Q62.5 — Duplication of ureter (ureter), Q63.0 — Accessory kidney (kidney with double pelvis), Q63.1 — Lobulated, fused and horseshoe kidney (kidneys), Q64.74 — Double urethra (urethra), Q64.75 — Double urinary meatus (urinary meatus), Q64.79 — Other congenital malformations of bladder and urethra (bladder), Q70.0 — Fused fingers (fingers), Q70.2 — Fused toes (toes), Q74.0 — Other congenital malformations of upper limb(s), including shoulder girdle (limb, congenital, upper), Q74.1 — Congenital malformation of knee (patella), Q74.2 — Other congenital malformations of lower limb(s), including pelvic girdle (astragaloscaphoid), Q74.8 — Other specified congenital malformations of limb(s) (limb, congenital), Q76.49 — Other congenital malformations of spine, not associated with scoliosis (spine NEC, congenital), Q76.6 — Other congenital malformations of ribs (ribs), Q79.8 — Other congenital malformations of musculoskeletal system (bone), Q79.9 — Congenital malformation of musculoskeletal system, unspecified (bone), Z98.1 — Arthrodesis status (spine NEC, arthrodesis status), +55 more

Contextual Map

Every relationship of Q89.4 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.

Hierarchy

• Q00-QA1 — Chapter 17: Congenital Malformations, Deformations and Chromosomal Abnormalities (Q00-QA1) (Q00-QA1)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q80-Q89 — Other congenital malformations[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Clinical classification (CCSR)

• MAL010 — Other specified and unspecified congenital anomalies[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

MS-DRG Grouper

• MCC — Major Complication or Comorbidity [MS-DRG severity]: “As a secondary diagnosis this code can raise the stay's MS-DRG severity tier (MCC).”— CMS MS-DRG Definitions Manual (Appendix C) · FY2026
• DRG 393 — OTHER DIGESTIVE SYSTEM DIAGNOSES WITH MCC[MS-DRG]: “OTHER DIGESTIVE SYSTEM DIAGNOSES WITH MCC (MDC 06)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 394 — OTHER DIGESTIVE SYSTEM DIAGNOSES WITH CC[MS-DRG]: “OTHER DIGESTIVE SYSTEM DIAGNOSES WITH CC (MDC 06)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 395 — OTHER DIGESTIVE SYSTEM DIAGNOSES WITHOUT CC/MCC[MS-DRG]: “OTHER DIGESTIVE SYSTEM DIAGNOSES WITHOUT CC/MCC (MDC 06)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 791 — PREMATURITY WITH MAJOR PROBLEMS[MS-DRG]: “PREMATURITY WITH MAJOR PROBLEMS (MDC 15)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 793 — FULL TERM NEONATE WITH MAJOR PROBLEMS[MS-DRG]: “FULL TERM NEONATE WITH MAJOR PROBLEMS (MDC 15)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

MDC crossing

• MDC 06 — Diseases and Disorders of the Digestive System[MDC crossing]: “Diseases and Disorders of the Digestive System — 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. 5,744 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026
• MDC 15 — Newborns and Other Neonates with Conditions Originating in Perinatal Period[MDC crossing]: “Newborns and Other Neonates with Conditions Originating in Perinatal Period — 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.”— CMS MS-DRG Definitions Manual · FY2026

Index entries (18)

• Conjoined twins[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Craniopagus[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Dicephalus, dicephaly[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Double, monster[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Epignathus[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Fusion, fused (congenital), twins[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Ischiopagus[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Janiceps[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• and 10 more

Nearest codes (12)

• Q89 — Other congenital malformations, not elsewhere classified[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q89.0 — Congenital absence and malformations of spleen[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q89.01 — Asplenia (congenital)[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q89.09 — Congenital malformations of spleen[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q89.1 — Congenital malformations of adrenal gland[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q89.2 — Congenital malformations of other endocrine glands[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q89.3 — Situs inversus[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• Q89.7 — Multiple congenital malformations, not elsewhere classified[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• and 4 more

Change history

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

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 FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v43.1 (April 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 — v43 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 structured 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 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.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Nearest Codes in This Family

Official ICD-10-CM classifications closest to Q89.4 in its code family, with their registry titles.

• Q89.01 — Asplenia (congenital)
• Q89.09 — Congenital malformations of spleen
• Q89.1 — Congenital malformations of adrenal gland
• Q89.2 — Congenital malformations of other endocrine glands
• Q89.3 — Situs inversus
• Q89.7 — Multiple congenital malformations, not elsewhere classified
• Q89.8 — Other specified congenital malformations
• Q89.81 — Kabuki syndrome
• Q89.89 — Other specified congenital malformations
• Q89.9 — Congenital malformation, unspecified

View all codes in the Q89 family