The most common denial reasons in OB/GYN billing, ranked by frequency, with practical prevention steps for each.
Denials rarely come from one dramatic mistake — they come from a handful of small, repeatable errors that show up across hundreds of claims a month. Here are the seven most common denial reasons we see in OB/GYN billing, and what actually prevents each one.
1. Eligibility Not Verified at Time of Service
Coverage lapses and plan changes are the single most preventable denial cause. A same-day eligibility check, not just one done at scheduling, closes this gap. Our [eligibility verification best practices](/blog/eligibility-verification-best-practices) guide covers exactly how to build this into front-desk workflow.
2. Missing or Incorrect Prior Authorization
Certain procedures — many gynecological surgeries and some infertility treatments — require authorization before the claim is even submitted. See our breakdown of [which OB/GYN procedures typically require prior authorization](/blog/prior-authorization-obgyn-procedures).
3. Bundled Service Denials (CO-97)
Billing a service separately that the payer considers bundled into another. Our dedicated guide on [CO-97 denials](/blog/co-97-denial-code-explained) covers this in depth.
4. Unspecified or Missing Trimester Codes
O-codes without the correct trimester digit are an easy, avoidable denial trigger — see our [ICD-10 O-codes guide](/blog/icd-10-o-codes-guide).
5. Global Period Conflicts
Billing a follow-up visit separately during a procedure's global period, when it should be bundled.
6. Credentialing Gaps
Claims submitted under a provider not yet fully credentialed with that specific payer are denied outright, regardless of medical necessity. See our [credentialing checklist](/blog/credentialing-checklist-new-obgyn).
7. Timely Filing Limits
Every payer has a filing deadline, and OB/GYN claims — with their bundled, delayed-submission nature — are especially vulnerable to missing it.
Key Takeaways
- ›Most denials trace back to front-end verification gaps, not coding errors
- ›Fixing the top 2-3 reasons usually resolves the majority of denial volume
- ›Denial patterns should be reviewed monthly, not just when cash flow tightens
A structured [denial management](/denial-management) process — one that categorizes and trends denials rather than just resubmitting them — is what separates practices with a shrinking denial rate from ones stuck fighting the same fires every month.