O31.8X21 Other complications specific to multiple gestation, second trimester, fetus 1

Billable ICD-10-CM code, FY2026.

Built from O31.8X2 with 7th character 1 (fetus 1).

Applies from O31 Complications specific to multiple gestation

Excludes2 (not included here)

• delayed delivery of second twin, triplet, etc. (O63.2)
• malpresentation of one fetus or more (O32.9)
• placental transfusion syndromes (O43.0-)

7th character note

• One of the following 7th characters is to be assigned to each code under category O31. 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 O31 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.

Nearby codes

• O31.8X14 Other complications specific to multiple gestation, first trimester, fetus 4
• O31.8X15 Other complications specific to multiple gestation, first trimester, fetus 5
• O31.8X19 Other complications specific to multiple gestation, first trimester, other fetus
• O31.8X2 Other complications specific to multiple gestation, second trimester
• O31.8X20 Other complications specific to multiple gestation, second trimester, not applicable or unspecified
• O31.8X21 Other complications specific to multiple gestation, second trimester, fetus 1 (this code)
• O31.8X22 Other complications specific to multiple gestation, second trimester, fetus 2
• O31.8X23 Other complications specific to multiple gestation, second trimester, fetus 3
• O31.8X24 Other complications specific to multiple gestation, second trimester, fetus 4
• O31.8X25 Other complications specific to multiple gestation, second trimester, fetus 5
• O31.8X29 Other complications specific to multiple gestation, second trimester, other fetus