What does ICD-10 code Q91 mean?

ICD-10 code Q91 is the standardized code used for trisomy 18 and trisomy 13 in medical records and coding systems.

When is ICD-10 code Q91 used?

Doctors, hospitals, and insurers may use ICD-10 code Q91 when recording trisomy 18 and trisomy 13 in a standardized format. This entry may also act as a broader category that points toward more specific child codes.

Does ICD-10 code Q91 confirm a diagnosis?

No. A code helps standardize documentation and claims, but it should not be read as a substitute for a clinician's full assessment.

ICD10

ICD-10 Code Q91: Trisomy 18 and Trisomy 13

Name: ICD-10 Code Q91: Trisomy 18 and Trisomy 13
Creator: HealthAssure Clinical Team
Published: 2026-05-21T06:30:11.959Z

Q91 is an ICD-10 diagnosis entry used to group records related to Trisomy 18 and Trisomy 13. You may see this entry in coding references, medical records, or claims workflows when a broader diagnosis category is being reviewed before a more specific code is chosen. ICD-10 entries help standardize how diagnoses are organized for coding, reporting, analytics, and documentation. This code sits within the broader ICD-10 area for Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (Q00-QA0).

Reviewed by HealthAssure Clinical TeamUpdated 21 May 2026

What is this code?

ICD-10 entries help standardize how diagnoses are organized for coding, reporting, analytics, and documentation. This code sits within the broader ICD-10 area for Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (Q00-QA0).

When is it used?

May be used when a clinician documents trisomy 18 and trisomy 13 in a patient's medical record.
May appear in hospital records, claims, referrals, and clinical documentation.
This code may act more like a grouping or parent code, so a more specific child code may be used in final documentation when available.

What it does not mean

A code alone does not explain severity, treatment plan, or outcome.
A medical code should not be treated as a substitute for a doctor's diagnosis or advice.
This entry may represent a broader category rather than the most specific billable code.

Code hierarchy

chapter

17Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (Q00-QA0)

block

Q90-Q99Chromosomal abnormalities, not elsewhere classified

currentQ90-Q99

Where you may see this code

You may see this entry in coding references, medical records, or claims workflows when a broader diagnosis category is being reviewed before a more specific code is chosen.

Sibling codes

Q90Down syndrome Q92Other trisomies and partial trisomies of the autosomes, not elsewhere classified Q93Monosomies and deletions from the autosomes, not elsewhere classified Q95Balanced rearrangements and structural markers, not elsewhere classified Q96Turner's syndrome Q97Other sex chromosome abnormalities, female phenotype, not elsewhere classified Q98Other sex chromosome abnormalities, male phenotype, not elsewhere classified Q99Other chromosome abnormalities, not elsewhere classified

Coding guidelines

Compatibility

Legacy code aligns to an official FY 2026 category. Frontend should resolve to the official category page and surface the billable child codes.

Legacy codes

Q91

Replacement codes

Q91.0 — Trisomy 18, nonmosaicism (meiotic nondisjunction)Q91.1 — Trisomy 18, mosaicism (mitotic nondisjunction)Q91.2 — Trisomy 18, translocationQ91.3 — Trisomy 18, unspecifiedQ91.4 — Trisomy 13, nonmosaicism (meiotic nondisjunction)Q91.5 — Trisomy 13, mosaicism (mitotic nondisjunction)Q91.6 — Trisomy 13, translocationQ91.7 — Trisomy 13, unspecified

Common synonyms

Trisomy 18 and Trisomy 13

Frequently asked questions

About this content

This page is prepared by HealthAssure's clinical team using official coding standards from ICD-10. AI tools assist with drafting explanations, which are then reviewed and verified by healthcare professionals for accuracy. This content is for informational purposes and does not replace professional medical advice. Meet our team.