Denials are the most visible symptom of revenue cycle problems — and in OB/GYN, they cluster around a predictable set of causes. The good news: most are preventable once you know where they come from. Here are the nine denial reasons we see most often in OB/GYN billing, what causes each, and how to prevent them.
1. Eligibility and coverage problems
Typical codes: CO-27 (coverage terminated), CO-31 (patient not identified), CO-22 (another payer primary), CO-109 (not covered by this payer)
Causes: outdated insurance on file, coverage changes mid-pregnancy, wrong primary/secondary order, Medicaid plan assignment changes.
Prevention: verify eligibility before every visit, re-verify during pregnancy, confirm coordination of benefits with patients at check-in, and check Medicaid managed care assignment monthly for obstetric patients. See eligibility verification.
2. Missing or mismatched prior authorization
Typical codes: CO-197 (precertification/authorization absent), CO-198 (precertification exceeded)
Causes: no authorization requested, authorization for a different CPT code than billed, expired authorization, procedure changed in the OR.
Prevention: an authorization checklist by payer, authorization matched to planned CPT codes, and a process to update authorizations within the payer's window when the procedure changes. See which OB/GYN procedures require prior authorization.
3. Bundling denials (CO-97)
Typical code: CO-97 (service included in payment for another service)
Causes: routine visits billed during the global obstetric package, routine post-op visits billed in a surgical global period, NCCI code pairs without supporting modifiers, E/M with minor procedures without modifier 25.
Prevention: global period tracking, NCCI edits in the claim scrubber, and modifiers applied only with documentation. Read our full CO-97 denial code guide.
4. Diagnosis errors
Typical codes: CO-11 (diagnosis inconsistent with procedure), CO-16 (claim lacks information), CO-146 (diagnosis invalid for date of service)
Causes: missing or wrong trimester characters, Z34 used with O codes, missing Z37 on delivery claims, O80 misused, outdated codes after the October 1 ICD-10-CM update, non-pregnancy diagnoses on obstetric services.
Prevention: scrubber edits for Chapter 15 rules, annual code updates loaded on time, and provider templates that update diagnoses at each visit. See multiple O codes sequencing.
5. Global period conflicts
Typical codes: CO-97, CO-B15 (procedure qualifying service not paid or identified)
Causes: visits during surgical global periods without modifier 24, procedures without 58, 78 or 79, prenatal visits billed outside the package without a complication diagnosis.
Prevention: global period flags in the PM system, 99024 for routine post-op visits, and clear documentation for unrelated problems.
6. Credentialing gaps
Typical codes: CO-B7 (provider not certified/eligible for this procedure or date), out-of-network denials, CO-242 (services not provided by network/primary care providers)
Causes: new providers billing before enrollment is effective, lapsed re-credentialing or CAQH attestation, new locations not added, taxonomy mismatches.
Prevention: an enrollment tracker by provider and payer, holding claims until effective dates are confirmed, and re-credentialing reminders. See credentialing.
7. Timely filing
Typical code: CO-29 (time limit for filing has expired)
Causes: global OB claims held too long after delivery, slow charge entry, claims rejected at the clearinghouse and never resubmitted, secondary claims not filed after primary payment.
Prevention: know each payer's limit, monitor claims with no response, fix rejections the same day, and keep proof of timely filing (clearinghouse acceptance reports).
8. Medical necessity
Typical code: CO-50 (not deemed a medical necessity)
Causes: ultrasounds beyond payer frequency limits without high-risk indications, surgery without documentation that meets payer criteria, diagnosis codes that don't support the service.
Prevention: know payer medical policies for high-volume services (OB ultrasound, hysterectomy, infertility), link diagnoses accurately, and document indications. See our OB ultrasound billing guide.
9. Duplicate claims
Typical code: CO-18 (exact duplicate claim/service)
Causes: resubmitting instead of sending a corrected claim, or two providers billing the same global package.
Prevention: use corrected claims (frequency code 7) or voids (frequency code 8), and coordinate with other practices in split-care pregnancies.
How to tell which denials matter most
Count denials by reason and by dollar value each month. A reason with few denials but high dollars (for example, surgical authorization denials) may deserve attention before a frequent, low-dollar reason. Then look for the upstream process behind the top two or three reasons and fix it. Track the trend to confirm the fix worked.
| Denial category | Upstream owner |
|---|---|
| Eligibility / COB | Front desk, verification team |
| Authorization | Surgical scheduler, verification team |
| Bundling / modifiers | Coding, providers |
| Diagnosis | Providers, coding |
| Credentialing | Credentialing coordinator |
| Timely filing | Billing team |
| Medical necessity | Providers, coding |
Key takeaways
- Most OB/GYN denials come from a handful of repeatable causes.
- Front-end problems can't be fixed by better coding later.
- Work denials quickly — and fix the cause, not just the claim.
- Measure denials by reason and dollars every month.
A monthly denial review agenda
- Totals: number and dollar value of denials, compared to last month
- Top five reasons by dollars, with trend
- By payer: any payer with a sudden change
- By provider: any provider with an unusual pattern
- Fixes in progress: what was changed last month and whether it worked
- New actions: one or two process changes for the coming month
Thirty minutes a month with this agenda is often enough to cut repeat denials substantially over time.
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Frequently asked questions
What's the most common reason OB/GYN claims are denied?
It varies by practice, but front-end issues — eligibility, coordination of benefits and authorization — and bundling denials such as CO-97 are consistently among the most common.
How can a practice prevent denials?
Verify eligibility before every visit and during pregnancy, match authorizations to planned CPT codes, scrub claims for OB/GYN-specific errors, track global periods, monitor credentialing, and review denials monthly by root cause.
Should every denial be appealed?
No. Every denial should be reviewed. Some need a corrected claim, some a reconsideration or appeal, and some are correct and should be adjusted — with the cause fixed upstream.
How quickly should denials be worked?
Ideally within two business days of the remittance. Faster work preserves appeal windows and keeps days in A/R down.
Disclaimer:This article is for general educational purposes and reflects coding rules and payer policies as we understand them on the date shown. Always confirm against the current CPT and ICD-10-CM code sets and your payers' published policies.
