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ICD-10-CM 2027 diagnosis code

O99.321Drug use complicating pregnancy, first trimester

✓ Billable / specificCC — complication/comorbidityMaternity · age 9–64Female only

O99.321 is a valid, billable ICD-10-CM code for drug use complicating pregnancy, first trimester. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.

Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About O99.321

O99.321 is the ICD-10-CM diagnosis code for drug use complicating pregnancy, first trimester. It belongs to category O99 (other maternal diseases classifiable elsewhere but complicating pregnancy, childbirth and the puerperium), block O94-O9A (other obstetric conditions, not elsewhere classified) and chapter 15 (pregnancy, childbirth and the puerperium). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within O99.32 (drug use complicating pregnancy, childbirth, and the puerperium), O99.321 is specifically for drug use complicating pregnancy, first trimester. Related codes cover pregnancy, unspecified trimester (O99.320), pregnancy, second trimester (O99.322), pregnancy, third trimester (O99.323), childbirth (O99.324) and the puerperium (O99.325).

Use an additional code to identify specific condition.

As a secondary diagnosis it is a CC (complication or comorbidity), which can move an inpatient stay into the "with CC" MS-DRG of its family, unless the principal diagnosis excludes it.

In MS-DRG v44.0, it is part of the grouping logic for DRG 817 (Other Antepartum Diagnoses with O.R. Procedures with MCC, relative weight 2.0534), DRG 818 (Other Antepartum Diagnoses with O.R. Procedures with CC, relative weight 1.2942), DRG 819 (Other Antepartum Diagnoses with O.R. Procedures without CC/MCC, relative weight 0.7739), DRG 831 (Other Antepartum Diagnoses without O.R. Procedures with MCC, relative weight 1.1558), DRG 832 (Other Antepartum Diagnoses without O.R. Procedures with CC, relative weight 0.7585) and DRG 833 (Other Antepartum Diagnoses without O.R. Procedures without CC/MCC, relative weight 0.5002), in MDC 14 (Pregnancy, Childbirth and the Puerperium), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

The Medicare Code Editor treats this as a maternity diagnosis, expected only for patients age 9 through 64.

It is on the CMS list of diagnoses consistent only with female patients (the sex-conflict edit itself was retired in FY2025).

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as 648.31 (drug dependence of mother, delivered, with or without mention of antepartum condition) and 648.33 (drug dependence of mother, antepartum condition or complication).

Notes that apply from higher levels

Instructions written at a parent level also apply to O99.321.

› From O99.32 Drug use complicating pregnancy, childbirth, and the puerperium
Use additional code
  • code(s) from F11-F16 and F18-F19 to identify manifestations of the drug use
› From O99 Other maternal diseases classifiable elsewhere but complicating pregnancy, childbirth and the puerperium
Includes
  • conditions which complicate the pregnant state, are aggravated by the pregnancy or are a main reason for obstetric care
Excludes2
  • when the reason for maternal care is that the condition is known or suspected to have affected the fetus (O35-O36)
Use additional code
  • code to identify specific condition

Broader instructions also apply from Chapter 15: Pregnancy, childbirth and the puerperium.

MS-DRG v44.0 grouping

All DRGs →

Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.

ICD-9-CM equivalent

Converter →
  • 648.31Drug dependence of mother, delivered, with or without mention of antepartum conditionapproximate
  • 648.33Drug dependence of mother, antepartum condition or complicationapproximate

From the CMS 2018 General Equivalence Mappings (GEMs), the final GEMs release.

Code history

  1. 2016
  2. 2017
  3. 2018
  4. 2019
  5. 2020
  6. 2021
  7. 2022
  8. 2023
  9. 2024
  10. 2025
  11. 2026
  12. 2027
  • FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
  • No changes since FY2016.

Common questions about O99.321

Is O99.321 billable?

Yes. O99.321 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).

Can O99.321 be used as a principal diagnosis?

Yes. The Medicare Code Editor doesn't restrict O99.321 as a principal diagnosis.

Is O99.321 a CC or MCC?

O99.321 is a CC (complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.

What DRG does O99.321 group to?

O99.321 is used in the MS-DRG v44.0 logic for MS-DRG 817 (Other Antepartum Diagnoses with O.R. Procedures with MCC), MS-DRG 818 (Other Antepartum Diagnoses with O.R. Procedures with CC), MS-DRG 819 (Other Antepartum Diagnoses with O.R. Procedures without CC/MCC), MS-DRG 831 (Other Antepartum Diagnoses without O.R. Procedures with MCC), MS-DRG 832 (Other Antepartum Diagnoses without O.R. Procedures with CC) and MS-DRG 833 (Other Antepartum Diagnoses without O.R. Procedures without CC/MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.

What is the ICD-9 code for O99.321?

The CMS General Equivalence Mappings map O99.321 to ICD-9-CM 648.31 and 648.33.