2026 ICD-10-CM Diagnosis Code O21.0Mild hyperemesis gravidarum

ICD-10-CM Codes›O00-O9A›O20-O29›O21

ICD-10-CM O21.0
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

O21.0 is a billable ICD-10-CM diagnosis code for mild hyperemesis gravidarum. 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). Coders also document this condition as hyperemesis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified complications in pregnancy.

This medical diagnosis code is frequently used in OB/GYN medical specialties to designate conditions such maternal disorders related to pregnancy.

Code Identity

ICD-10-CM Code
O21.0
Billable Status
Yes — Valid for Submission
Code Describes
Mild hyperemesis gravidarum
Short Description
Mild hyperemesis gravidarum
Same as the full description in the CMS dataset.
Parent Code
O21
Excessive vomiting in pregnancy

Code Classification

ChapterO00-O9APregnancy, childbirth and the puerperium
SectionO20-O29Other maternal disorders predominantly related to pregnancy
CategoryO21Excessive vomiting in pregnancy
This CodeO21.0Mild hyperemesis gravidarum

Code EditsBilling

Medicare Code Editor checks that affect claim validity for O21.0.

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).

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Hyperemesis
  • Hyperemesis gravidarum
  • Mild hyperemesis gravidarum
  • Moderate hyperemesis gravidarum

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Hyperemesis gravidarum, mild or unspecified, starting before the end of the 20th week of gestation

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Hyperemesis
      • gravidarum (mild)
    • Pregnancy(single) (uterine)
      • complicated by (care of) (management affected by)
        • hyperemesis (gravidarum) (mild)
    • Pregnancy(single) (uterine)
      • complicated by (care of) (management affected by)
        • vomiting
          • hyperemesis gravidarum (mild)

Clinical ClassificationClinical

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

CCSR PRG028
Other specified complications in pregnancy
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Hyperemesis Gravidarum

    intractable vomiting that develops in early pregnancy and persists. this can lead to dehydration and weight loss.

Patient EducationClinical

Health Problems in Pregnancy

A health problem in pregnancy is any disease or condition that could affect your health or the health of your fetus. Some health problems may make it more likely that you will have a high-risk pregnancy. A high-risk pregnancy is one in which you, your fetus, or both are at higher risk for health problems than in a typical pregnancy.

The full article covers:

  • What are health problems in pregnancy?
  • What raises my risk for health problems during pregnancy?
  • Can chronic health conditions cause problems in pregnancy?
  • Can health problems in pregnancy be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert O21.0 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
643.03 Mild hyperemesis-antepar
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About O21.0Overview

Is O21.0 (Excessive vomiting in pregnancy) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report mild hyperemesis gravidarum on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does O21.0 group to?

When mild hyperemesis gravidarum 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 O21.0 be reported for?

The Medicare Code Editor checks mild hyperemesis gravidarum against patient demographics: this code is intended for maternity cases (age 9 through 64). Claims outside these limits are flagged as inconsistent.

What is the ICD-9 equivalent of O21.0?

Under the General Equivalence Mappings, mild hyperemesis gravidarum converts to ICD-9-CM 643.03 (mild hyperemesis-antepar). The mapping is approximate, so confirm the match fits the documentation.

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.