O41.1231 Chorioamnionitis, third trimester, fetus 1

Billable ICD-10-CM code, FY2026.

Built from O41.123 with 7th character 1 (fetus 1).

Applies from O41 Other disorders of amniotic fluid and membranes

Excludes1 (never code together)

• encounter for suspected maternal and fetal conditions ruled out (Z03.7-)

7th character note

• One of the following 7th characters is to be assigned to each code under category O41. 7th character 0 is for single gestations and multiple gestations where the fetus is unspecified. 7th characters 1 through 9 are for cases of multiple gestations to identify the fetus for which the code applies. The appropriate code from category O30, Multiple gestation, must also be assigned when assigning a code from category O41 that has a 7th character of 1 through 9.

7th character required

• 0 — not applicable or unspecified
• 1 — fetus 1
• 2 — fetus 2
• 3 — fetus 3
• 4 — fetus 4
• 5 — fetus 5
• 9 — other fetus

Medicare Code Edits (MCE v43.1 (April 2026))

• Maternity diagnoses (age 9 through 64): Age conflict edit. These diagnoses are clinically expected only in patients age 9 through 64.

Code annotations containing back-references to O41.1231

Back-references to O41

• Type 1 Excludes: Z03.7 Encounter for suspected maternal and fetal conditions ruled out ("known or suspected fetal anomalies affecting management of mother, not ruled out (O26.-, O35.-, O36.-, O40.-, O41.-)")

Nearby codes

• O41.1224 Chorioamnionitis, second trimester, fetus 4
• O41.1225 Chorioamnionitis, second trimester, fetus 5
• O41.1229 Chorioamnionitis, second trimester, other fetus
• O41.123 Chorioamnionitis, third trimester
• O41.1230 Chorioamnionitis, third trimester, not applicable or unspecified
• O41.1231 Chorioamnionitis, third trimester, fetus 1 (this code)
• O41.1232 Chorioamnionitis, third trimester, fetus 2
• O41.1233 Chorioamnionitis, third trimester, fetus 3
• O41.1234 Chorioamnionitis, third trimester, fetus 4
• O41.1235 Chorioamnionitis, third trimester, fetus 5
• O41.1239 Chorioamnionitis, third trimester, other fetus