Q91.0 Trisomy 18, nonmosaicism (meiotic nondisjunction)

ICD-10-CM Code Q91.0: Trisomy 18, nonmosaicism (meiotic nondisjunction)

ICD-10-CM code Q91.0 identifies Trisomy 18, nonmosaicism (meiotic nondisjunction), an active diagnosis classified as a congenital abnormality or disease or syndrome. It falls under the parent category Q91 for Trisomy 18 and Trisomy 13, distinguishing it from other specified Trisomy 18 variants like translocation or unspecified presentations. 1 6

Plain-language overview

Code Q91.0 represents a congenital abnormality or disease and syndrome involving Trisomy 18, specifically nonmosaicism caused by meiotic nondisjunction, and its terminology record is currently active. 1

What this code represents

The Q91.0 code is a narrower concept within the ICD-10-CM hierarchy, operating under the parent concept Q91, which encompasses diagnoses for both Trisomy 18 and Trisomy 13. 1

Within the Q91 category, Q91.0 specifically denotes nonmosaicism via meiotic nondisjunction, distinguishing it from Q91.2 for translocation and Q91.3 for unspecified Trisomy 18. 6

Clinical context

Meiotic nondisjunction involves the failure of chromosomes to separate during meiosis, producing daughter cells with an abnormal number of chromosomes, such as an extra chromosome resulting in 47 total chromosomes. 2

Meiotic nondisjunction is noted as having greater clinical significance than mitotic nondisjunction because most aneuploidies resulting from meiotic errors are incompatible with life. 2

Documentation considerations

The terminology record for Q91.0 specifies the exact preferred name as Trisomy 18, nonmosaicism (meiotic nondisjunction), which differs from the translocation and unspecified Trisomy 18 variants listed under the same parent category. 1 6

What the sources add

While the terminology record defines Q91.0 as a specific nonmosaic meiotic nondisjunction diagnosis, a separate phecode mapping list groups it alongside related nonmosaic and mosaic trisomy conditions. 1 3

The Q91.0 code appears in the Q91 category listing alongside translocation and unspecified Trisomy 18 variants, whereas broader CMS definitions manuals list generalized whole chromosome trisomy concepts without detailing Q91.0. 6 4

Coverage and utilization context

The CMS MS-DRG definitions manuals include generalized whole chromosome trisomy concepts within their code listings, but these specific manual excerpts do not contain the target code Q91.0 or define its coverage rules. 4 5

Sources

1. ICD-10-CM Q91.0 terminology record — National Cancer Institute Enterprise Vocabulary Services; accessed 2026-07-27.
2. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-27.
3. Phecode 758 · Cancer PRSweb — csg.sph.umich.edu; accessed 2026-07-27.
4. ICD-10-CM/PCS MS-DRG v34.0 Definitions Manual — cms.gov; accessed 2026-07-27.
5. ICD-10-CM/PCS MS-DRGv33 Definitions Manual — cms.gov; accessed 2026-07-27.
6. EVS Explore — evsexplore.semantics.cancer.gov; accessed 2026-07-27.