2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

O21.0 is a billable ICD-10-CM diagnosis code for mild hyperemesis gravidarum. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) 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

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to O21.0: its own notes plus those printed at block O20-O29 and Chapter 15. A note printed at a category, block or chapter applies to every code under it.

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

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

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From Chapter 15 (O00-O9A) Pregnancy, childbirth and the puerperium applies to 2,481 codes
  • supervision of normal pregnancy (Z34.-)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Block O20-O29 Other maternal disorders predominantly related to pregnancy applies to 260 codes
  • maternal care related to the fetus and amniotic cavity and possible delivery problems (O30-O48)
  • maternal diseases classifiable elsewhere but complicating pregnancy, labor and delivery, and the puerperium (O98-O99)
From Chapter 15 (O00-O9A) Pregnancy, childbirth and the puerperium applies to 2,481 codes
  • mental and behavioral disorders associated with the puerperium (F53.-)
  • obstetrical tetanus (A34)
  • postpartum necrosis of pituitary gland (E23.0)
  • puerperal osteomalacia (M83.0)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 15 (O00-O9A) Pregnancy, childbirth and the puerperium applies to 2,481 codes
  • code, if applicable, from category Z3A, Weeks of gestation, to identify the specific week of the pregnancy, if known.

Notes

General instructions on how these codes are used.

From Chapter 15 (O00-O9A) Pregnancy, childbirth and the puerperium applies to 2,481 codes
  • CODES FROM THIS CHAPTER ARE FOR USE ONLY ON MATERNAL RECORDS, NEVER ON NEWBORN RECORDS
  • Codes from this chapter are for use for conditions related to or aggravated by the pregnancy, childbirth, or by the puerperium (maternal causes or obstetric causes)
  • Trimesters are counted from the first day of the last menstrual period. They are defined as follows:
  • 1st trimester- less than 14 weeks 0 days
  • 2nd trimester- 14 weeks 0 days to less than 28 weeks 0 days
  • 3rd trimester- 28 weeks 0 days until delivery

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name O21.0, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming O21.0: they are not reported together with it, unless the two conditions are unrelated.

  • R11 Nausea and vomiting
    excessive vomiting in pregnancy (O21.-) names O21.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About O21.0Overview

What is the ICD-10 code for mild hyperemesis gravidarum?

The ICD-10-CM code for mild hyperemesis gravidarum is O21.0 (sometimes written as O210). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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 833, 832, 831, 819, 818, 817, with relative weights from 0.5000 to 1.7586 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.