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Practice Tool — Chapter O
Maternity Coding Navigator
Step-by-step guidance for ICD-10-CM Chapter O — trimester, episode of care, delivery codes, outcome of delivery (Z37), weeks of gestation (Z3A), and fetus identification for multiple gestations.
FY2027 update in progress. The FY2027 ICD-10-CM code set (effective 10/01/2026) is still loading, so a code may be missing or a deleted code may still show. Confirm against official CMS files before billing.
Chapter O Quick Reference
Trimester Definitions
1st trimesterLess than 14 weeks
2nd trimester14 weeks – <28 weeks
3rd trimester28 weeks through delivery
Guideline I.C.15.a
Episode of Care (7th Character)
0Unspecified (use only if episode not applicable)
1Fetus 1 (multiple gestation)
2Fetus 2 (multiple gestation)
3–5Fetus 3, 4, 5
9Other fetus (unspecified)
For single gestation, no fetus ID needed
Always Add at Delivery
Z37.x Outcome of delivery — required on mother's record for every delivery encounter
Z3A.xx Weeks of gestation — required as secondary code on every O-chapter delivery
Guideline I.C.15.b.4 & I.C.15.a.1
⚠ Critical Coding Rules — Chapter O
- The obstetric chapter takes sequencing priority — O codes are listed first, non-obstetric conditions second (Guideline I.C.15.a.2)
- A code from category O80 (encounter for full-term uncomplicated delivery) can only be used alone — no other O codes with it
- Pre-existing conditions complicating pregnancy use O codes, not the underlying condition code as principal
- For postpartum complications: use O codes for conditions arising within 6 weeks of delivery; beyond 6 weeks, non-obstetric codes apply
- HIV in pregnancy: sequence O98.7– first, then B20, then any HIV-related conditions
Step-by-Step Navigator
Enter documented weeks of gestation. Z3A codes range Z3A.22–Z3A.42+.
The 7th character identifies which fetus the complication affects in a multiple gestation.
Coding Guidance
Required Additional Codes
Sequencing Guidance
📋 Documentation to Verify
Common Scenarios — Code Sets at a Glance
Normal term delivery — no complications
Code Set (sequence in this order):
O80 — Encounter for full-term uncomplicated delivery
Z37.0 — Single liveborn infant
Z3A.39 — 39 weeks gestation (adjust to documented weeks)
⚠ O80 must be used alone — no other O-chapter codes permitted with it.
Gestational hypertension — 3rd trimester
Antepartum encounter:
O13.3 — Gestational [pregnancy-induced] hypertension, third trimester
Z34.3x — Encounter for supervision of normal third trimester pregnancy
If delivered this encounter:
O13.3 — Principal (complication present at delivery)
Z37.0 — Outcome of delivery
Z3A.3x — Weeks gestation
Preeclampsia with severe features — delivery encounter
Code Set:
O14.13 — Severe pre-eclampsia, third trimester
O82 — C-section (if applicable)
Z37.0 — Single liveborn
Z3A.3x — Weeks gestation
Note: O14.2 = HELLP syndrome. If HELLP is documented, use O14.2 + O14.13 for severe features.
Gestational diabetes — antepartum visit
Key distinction — gestational vs. pre-existing:
Gestational diabetes (developed during pregnancy):
O24.410 — Diet controlled, antepartum
O24.414 — Insulin controlled, antepartum
O24.415 — Oral hypoglycemic drugs, antepartum
Pre-existing Type 1 complicating pregnancy:
O24.01x — 1st trimester
O24.02x — 2nd trimester
O24.03x — 3rd trimester
+ E10.xxx for the Type 1 DM manifestations
Cesarean delivery — prior C-section scar
Repeat C-section code set:
O34.21 — Low transverse uterine scar (most common)
or O34.22 — Low vertical scar
O82 — C-section delivery
Z37.0 — Single liveborn
Z3A.3x — Weeks gestation
O34.21 is the principal for the scar as reason for C-section. O82 added for the delivery itself.
Postpartum hemorrhage
PPH code set:
O72.0 — Third-stage hemorrhage (placenta not yet delivered)
O72.1 — Other immediate postpartum hemorrhage (placenta delivered, within 24 hrs)
O72.2 — Delayed/secondary postpartum hemorrhage (after 24 hrs)
If uterine atony: O72.1 is the appropriate code — atony is the most common cause and the hemorrhage code captures it.
Blood transfusion given: add 30233N1 procedure code (ICD-10-PCS) or appropriate CPT.
Twin delivery — one liveborn, one stillborn
Outcome of delivery (Z37) for twins:
Z37.3 — Twins, both liveborn
Z37.4 — Twins, one liveborn and one stillborn
Z37.5 — Twins, both stillborn
Z37.6x — Other multiple births, all liveborn
Z37.7x — Other multiple births, some liveborn
Z37.8x — Other multiple births, all stillborn
Use the 7th character (1–9) on applicable O codes to identify which fetus has the complication.
Z37 — Outcome of Delivery Reference
| Code | Description |
|---|---|
| Z37.0 | Single liveborn infant, vaginal delivery |
| Z37.1 | Single stillborn infant |
| Z37.2 | Twins, both liveborn |
| Z37.3 | Twins, one liveborn and one stillborn |
| Z37.4 | Twins, both stillborn |
| Z37.50 | Multiple births NOS, all liveborn |
| Z37.51 | Triplets, all liveborn |
| Z37.52 | Quadruplets, all liveborn |
| Z37.59 | Other multiple births, all liveborn |
| Z37.60 | Multiple births NOS, some liveborn |
| Z37.61 | Triplets, some liveborn |
| Z37.62 | Quadruplets, some liveborn |
| Z37.69 | Other multiple births, some liveborn |
| Z37.7 | Other multiple births, all stillborn |
| Z37.9 | Outcome of delivery, unspecified |