O91.211Nonpurulent mastitis associated with pregnancy, first trimester

O91.211 is the ICD-10-CM diagnosis code for Nonpurulent mastitis associated with pregnancy, first trimester. It belongs to category O91 (infections of breast associated with pregnancy, the puerperium and lactation), block O85-O92 (complications predominantly related to the puerperium) 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 O91.21 (Nonpurulent mastitis associated with pregnancy), O91.211 is specifically for Nonpurulent mastitis associated with pregnancy, first trimester. Related codes cover second trimester (O91.212), third trimester (O91.213) and unspecified trimester (O91.219).

Use an additional code to identify infection.

It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.

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 675.21 (Nonpurulent mastitis associated with childbirth, delivered, with or without mention of antepartum condition) and 675.23 (Nonpurulent mastitis associated with childbirth, antepartum condition or complication).