2027 ICD-10-CM Diagnosis Code O00.521Right cornual ectopic pregnancy with intrauterine pregnancy
ICD-10-CM Codes›O00-O9A›O00-O08›O00
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- New 2027 Code
O00.521 is a billable ICD-10-CM diagnosis code for right cornual ectopic pregnancy with intrauterine pregnancy. 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. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 34 closely related codes. The code is restricted by the Medicare Code Editor to maternity cases (age 9 through 64).
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for O00.521.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to O00.521: its own notes plus those printed at O00, block O00-O08, and Chapter 15. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- ruptured ectopic pregnancy
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- 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.
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code from category O08 to identify any associated complication
- 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.
- 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 O00.521, its category, or a range that includes it.
Excludes1 11
These codes carry an Excludes1 note naming O00.521: they are not reported together with it, unless the two conditions are unrelated.
- G08 Intracranial and intraspinal phlebitis and thrombophlebitis
- K65 Peritonitis
- Block N70-N77 Inflammatory diseases of female pelvic organs
- R34 Anuria and oliguria
- R55 Syncope and collapse
- R57 Shock, not elsewhere classified
- T79.0 Air embolism (traumatic)
- T79.1 Fat embolism (traumatic)
- T79.4 Traumatic shock
- T81.1 Postprocedural shock
- T81.7 Vascular complications following a procedure, not elsewhere classified
Excludes2 6
These codes carry an Excludes2 note naming O00.521: its condition is not part of those codes, and both may be reported when the patient has both.
- D65 Disseminated intravascular coagulation [defibrination syndrome]
- D68 Other coagulation defects
- I26 Pulmonary embolism
- K72 Hepatic failure, not elsewhere classified
- Block N17-N19 Acute kidney failure and chronic kidney disease
- Block N30-N39 Other diseases of the urinary system
Code First 6
These codes say to code first a condition named in the note, and O00.521 is one of the conditions named.
Clinical InformationClinical
Pregnancy, Ectopic
a potentially life-threatening condition in which embryo implantation occurs outside the cavity of the uterus. most ectopic pregnancies (>96%) occur in the fallopian tubes, known as tubal pregnancy. they can be in other locations, such as uterine cervix; ovary; and abdominal cavity (pregnancy, abdominal).
Code History & ChangesHistory
New Code O00.521 was added to the ICD-10-CM code set for FY 2027, effective October 1, 2026.
Replacement O00.521 replaces the following previously assigned code(s):
- O00.81 - Other ectopic pregnancy with intrauterine pregnancy
Questions About O00.521Overview
What is the ICD-10 code for right cornual ectopic pregnancy with intrauterine pregnancy?
The ICD-10-CM code for right cornual ectopic pregnancy with intrauterine pregnancy is O00.521 (sometimes written as O00521). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is O00.521 (Cornual ectopic pregnancy with intrauterine pregnancy) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report right cornual ectopic pregnancy with intrauterine pregnancy on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does O00.521 group to?
When right cornual ectopic pregnancy with intrauterine pregnancy 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.
Is O00.521 a CC or MCC?
CMS lists O00.521 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 34 closely related codes in its exclusion list.
Who can O00.521 be reported for?
The Medicare Code Editor checks right cornual ectopic pregnancy with intrauterine pregnancy against patient demographics: this code is intended for maternity cases (age 9 through 64). Claims outside these limits are flagged as inconsistent.
