ICD-10-CM > O00-O9A > O85-O92 > O91 > O91.2 O91.2 Nonpurulent mastitis associated with pregnancy, the puerperium and lactation Non-Billable/Non-Specific Codes O91.21Nonpurulent mastitis associated with pregnancyO91.211Nonpurulent mastitis associated with pregnancy, first trimesterO91.212Nonpurulent mastitis associated with pregnancy, second trimesterO91.213Nonpurulent mastitis associated with pregnancy, third trimesterO91.219Nonpurulent mastitis associated with pregnancy, unspecified trimesterO91.22Nonpurulent mastitis associated with the puerperiumO91.23Nonpurulent mastitis associated with lactation