O36.8321 Maternal care for abnormalities of the fetal heart rate or rhythm, second trimester, fetus 1

Billable ICD-10-CM code, FY2026.

Built from O36.832 with 7th character 1 (fetus 1).

Applies from O36 Maternal care for other fetal problems

Includes

• the listed conditions in the fetus as a reason for hospitalization or other obstetric care of the mother, or for termination of pregnancy

Excludes1 (never code together)

• encounter for suspected maternal and fetal conditions ruled out (Z03.7-)
• placental transfusion syndromes (O43.0-)

Excludes2 (not included here)

• labor and delivery complicated by fetal stress (O77.-)

7th character note

• One of the following 7th characters is to be assigned to each code under category O36. 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 O36 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

Applies from O36.83 Maternal care for abnormalities of the fetal heart rate or rhythm

Applicable to

• Maternal care for depressed fetal heart rate tones
• Maternal care for fetal bradycardia
• Maternal care for fetal heart rate abnormal variability
• Maternal care for fetal heart rate decelerations
• Maternal care for fetal heart rate irregularity
• Maternal care for fetal tachycardia
• Maternal care for non-reassuring fetal heart rate or rhythm

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 O36.8321

Back-references to O36

• Type 2 Excludes: O98 Maternal infectious and parasitic diseases classifiable elsewhere but complicating pregnancy, childbirth and the puerperium ("when the reason for maternal care is that the disease is known or suspected to have affected the fetus (O35-O36)")
• Type 2 Excludes: O99 Other maternal diseases classifiable elsewhere but complicating pregnancy, childbirth and the puerperium ("when the reason for maternal care is that the condition is known or suspected to have affected the fetus (O35-O36)")
• 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

• O36.8314 Maternal care for abnormalities of the fetal heart rate or rhythm, first trimester, fetus 4
• O36.8315 Maternal care for abnormalities of the fetal heart rate or rhythm, first trimester, fetus 5
• O36.8319 Maternal care for abnormalities of the fetal heart rate or rhythm, first trimester, other fetus
• O36.832 Maternal care for abnormalities of the fetal heart rate or rhythm, second trimester
• O36.8320 Maternal care for abnormalities of the fetal heart rate or rhythm, second trimester, not applicable or unspecified
• O36.8321 Maternal care for abnormalities of the fetal heart rate or rhythm, second trimester, fetus 1 (this code)
• O36.8322 Maternal care for abnormalities of the fetal heart rate or rhythm, second trimester, fetus 2
• O36.8323 Maternal care for abnormalities of the fetal heart rate or rhythm, second trimester, fetus 3
• O36.8324 Maternal care for abnormalities of the fetal heart rate or rhythm, second trimester, fetus 4
• O36.8325 Maternal care for abnormalities of the fetal heart rate or rhythm, second trimester, fetus 5
• O36.8329 Maternal care for abnormalities of the fetal heart rate or rhythm, second trimester, other fetus