2026 ICD-10-CM Diagnosis Code O35.13X1Maternal care for (suspected) chromosomal abnormality in fetus, Trisomy 21, fetus 1

ICD-10-CM Codes›O00-O9A›O30-O48›O35

ICD-10-CM O35.13X1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

O35.13X1 is a billable ICD-10-CM diagnosis code for maternal care for (suspected) chromosomal abnormality in fetus, Trisomy 21, fetus 1. The 7th character 1 identifies fetus 1 in a multiple gestation pregnancy. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 817 through 819, 831 through 833. The code is restricted by the Medicare Code Editor to maternity cases (age 9 through 64). In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Maternal care related to fetal conditions.

Code Identity

ICD-10-CM Code
O35.13X1
Billable Status
Yes — Valid for Submission
Code Describes
Maternal care for (suspected) chromosomal abnormality in fetus, Trisomy 21, fetus 1
Short Description
Mat care chromosomal abnlt in fetus, Trisomy 21, fetus 1
Parent Code
O35.13
Maternal care for (suspected) chromosomal abnormality in fetus, Trisomy 21

Code Classification

ChapterO00-O9APregnancy, childbirth and the puerperium
SectionO30-O48Maternal care related to the fetus and amniotic cavity and possible delivery problems
CategoryO35Maternal care for known or suspected fetal abnormality and damage
This CodeO35.13X1Maternal care for (suspected) chromosomal abnormality in fetus, Trisomy 21, fetus 1

Code EditsBilling

Medicare Code Editor checks that affect claim validity for O35.13X1.

Maternity diagnoses
The Medicare Code Editor detects inconsistencies in maternity cases by checking a patient's age and any diagnosis on the patient's record. The maternity code edits apply to patients age ange is 9–64 years inclusive (e.g., diabetes in pregnancy, antepartum pulmonary complication).

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR PRG013
Maternal care related to fetal conditions
Default principal diagnosis: inpatient Yes · outpatient Yes

Code History & ChangesHistory

Replacement O35.13X1 replaces the following previously assigned code(s):

  • O35.1XX1 - Maternal care for chromosomal abnormality in fetus, fetus 1
FY 2023AddedAdded to the ICD-10-CM code setEffective October 1, 2022.
FY 2024–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About O35.13X1Overview

Is O35.13X1 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report maternal care for (suspected) chromosomal abnormality in fetus, Trisomy 21, fetus 1 on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character 1 in O35.13X1 mean?

The final character 1 identifies the fetus in a multiple gestation pregnancy: this code reports maternal care for (suspected) chromosomal abnormality in fetus, Trisomy 21 for fetus 1.

What MS-DRG does O35.13X1 group to?

When maternal care for (suspected) chromosomal abnormality in fetus, Trisomy 21, fetus 1 is the principal diagnosis on an inpatient stay, it groups to MS-DRG 817, 818, 819, 831, 832, 833, with relative weights from 0.5229 to 1.6880 depending on complications. Higher weights mean higher Medicare reimbursement.

Who can O35.13X1 be reported for?

The Medicare Code Editor checks maternal care for (suspected) chromosomal abnormality in fetus, Trisomy 21, fetus 1 against patient demographics: this code is intended for maternity cases (age 9 through 64). Claims outside these limits are flagged as inconsistent.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.