2027 OB/GYN Billing Code Changes: What CMS’s Proposed Rule Means for Your Practice

What Are the 2027 OB/GYN Billing Code Changes?

As of July 2026, the CMS CY 2027 Physician Fee Schedule proposed rule introduces two competing pathways for obstetric billing starting January 1, 2027. The first is a new set of unbundled CPT codes developed by the AMA and ACOG that replace the global obstetric package with individual codes for each prenatal visit, delivery, and postpartum encounter. The second is a set of 15 proposed HCPCS G-codes that would preserve the existing bundled global payment structure as a parallel option. ACOG opposes the G-codes, warning that running both systems simultaneously would increase administrative burden and create billing confusion across payers.

Transition deadline approaching: ACOG recommends that payers begin accepting individual E/M codes with modifier TH for antepartum visits no later than September 1, 2026, which is roughly five weeks away.

Revenue impact on the table: CMS estimates that OB/GYN services will see a 1 to 2 percent reimbursement decrease in 2027 as the one-time 2.5 percent conversion factor increase from 2026 expires.

Comment window still open: The proposed rule is accepting public comments through September 14, 2026, meaning the final structure could still change before the rule is finalized this fall.

What CMS Proposed on July 14

On July 14, 2026, CMS released the CY 2027 Medicare Physician Fee Schedule proposed rule, designated CMS-1848-P. The rule covers payment policy changes for Medicare Part B services effective January 1, 2027. For OB/GYN practices, this proposed rule contains the most significant billing development in years.

The AMA and ACOG spent nearly two years developing a restructured coding framework for maternity care services. That framework deletes 17 legacy global obstetric CPT codes, including the widely used CPT 59400 (vaginal delivery with full OB care), 59510 (cesarean delivery with full OB care), and 59610 (VBAC with full OB care). In their place, 12 new codes and 6 revised codes create a granular, unbundled system where every prenatal visit, delivery service, and postpartum encounter is billed individually using E/M codes and new labor and delivery codes.

CMS included these new AMA/ACOG codes in the proposed rule. However, CMS also proposed creating 15 new HCPCS G-codes that would mirror the old global obstetric payment structure. CMS stated these G-codes would reduce disruption for practices and payers that are not ready for the unbundled system. The proposed conversion factor for 2027 is $33.17 for qualifying APM participants and $32.84 for non-qualifying providers, representing a decrease of 1.19 to 1.68 percent from 2026 rates. CMS specifically estimates that OB/GYN services will drop by 2 percent in the facility setting and 1 percent in the office setting.

The comment period closes September 14, 2026, and the final rule is expected later in the fall.

Who Do These Changes Apply To?

The 2027 coding restructure applies to every provider and billing entity that submits claims for maternity care services. If your practice bills any of the current global obstetric package codes, including CPT 59400, 59510, 59610, or 59618, this change directly affects your revenue cycle.

The scope includes solo OB/GYN practitioners and independent women’s health clinics, multi-provider obstetrics groups and high-volume delivery centers, maternal-fetal medicine practices billing high-risk obstetric services, family medicine physicians who provide obstetric care, certified nurse-midwives billing under the PFS, and any billing company or revenue cycle management partner handling maternity claims on behalf of these providers. Practices that handle only gynecological services and do not bill global obstetric codes are not directly affected by the maternity restructure, though the conversion factor decrease applies across the fee schedule.

The downstream effect extends beyond Medicare. Medicaid programs and private insurers frequently use the Medicare PFS as a benchmark for their own rates and coverage policies. Several state Medicaid programs, including North Carolina, have already issued transition guidance. In our experience matching providers with billing partners, the practices most at risk are mid-size groups where billing is handled by a small internal team that has never operated outside the global package framework. Practices managing high-risk pregnancy billing face added complexity because high-risk cases often involve split care across multiple providers, which the unbundled system handles very differently from the global package.

Why CMS Created a Dual Code Path

CMS’s stated rationale for proposing the 15 G-codes is to minimize disruption. The agency acknowledged that the transition from bundled to unbundled maternity billing is significant and that some practices and payers may not be operationally ready by January 1, 2027. The G-codes would give those entities a fallback path that preserves the familiar global payment structure while the industry adjusts.

ACOG disagrees with this approach. In a statement issued July 15, 2026, ACOG warned that running both systems simultaneously would cause greater disruption, not less. ACOG’s position is that the G-codes would undermine price transparency for patients, divide the patient population by which billing system their insurer chooses, and create confusion for OB/GYN billing staff who would need to maintain two parallel workflows. ACOG urged CMS to adopt the new CPT codes and make a clean break by not implementing the proposed G-codes.

The tension matters for practice managers because the final rule will determine whether your billing team needs to support one new code set or two. One question we hear constantly from practice managers is whether they should wait for the final rule or start transitioning now. The answer, based on the patterns we see across providers, is that waiting creates more risk than acting early, because the September 1 modifier TH deadline applies regardless of what CMS decides about the G-codes.

What Does a Dual Billing System Mean for OB/GYN Practices?

If CMS finalizes the G-codes, OB/GYN practices would face a billing environment where two distinct code sets describe the same clinical services. The following table illustrates the core differences:

Billing Element	Current/G-Code Path (Bundled)	New CPT Path (Unbundled)
Prenatal visits	Bundled into one global code (e.g., 59400)	Each visit billed individually with E/M codes + modifier TH
Delivery	Included in the global package	Billed separately with new labor and delivery codes
Postpartum care	Included in the global package	Billed separately with E/M codes
Split care	Antepartum-only codes (59425, 59426) + delivery-only codes	Each provider bills their own E/M visits and services individually
Documentation	Lower per-encounter requirements	Higher; each encounter needs full E/M-level documentation
Pricing transparency	Limited; patient sees one lump sum	Higher; each service has its own line item

The operational reality of a dual system is that a practice’s billing team would need to determine, for every maternity patient, which code set the patient’s insurer will accept. One payer may adopt the new CPT codes immediately, while another stays on the G-code global path. Across the billing companies we vet, a recurring pattern is that these payer-by-payer differences are where denials spike during coding transitions. The administrative overhead of managing two parallel workflows, with two documentation standards and two sets of payer rules, is exactly the kind of complexity that overwhelms small in-house billing teams.

What to Do Before January 2027

The transition has already started. ACOG’s recommended September 1, 2026 deadline for switching to E/M codes with modifier TH for new antepartum visits is the first operational milestone. Here is the preparation checklist:

1. Audit your current global OB billing volume. Identify how many active maternity patients are currently billed under CPT 59400, 59510, 59610, or 59618. This is your transition scope.
2. Contact your top five payers about modifier TH acceptance. Confirm whether each payer is ready to accept E/M codes with the TH modifier for antepartum visits starting September 1, 2026. Document what you hear.
3. Update EHR templates to support unbundled billing. Your electronic health record system needs templates that capture full E/M-level documentation for every prenatal and postpartum visit, not just the minimal notes the global package required.
4. Train billing staff on both code sets. Until the final rule is published, your team needs to understand both the new unbundled CPT framework and the proposed G-code global path.
5. Test claims with your primary payers. Submit test claims using the E/M + TH modifier workflow before September 1 to identify adjudication issues early.
6. Review your billing partner’s readiness. If you outsource billing, confirm that your billing company has a documented plan for the 2027 transition and can support both workflows if the G-codes are finalized.
7. Monitor the comment period. The public comment window closes September 14, 2026. The final rule, expected this fall, will determine whether the G-codes survive.

What Happens If Your Practice Does Not Prepare?

The risk is not theoretical. On January 1, 2027, the legacy global obstetric CPT codes are being deleted from the code set. If a practice submits a claim using CPT 59400 after that date, the claim will be rejected outright. There is no grace period for the code deletion.

Practices that delay preparation face several compounding problems. Claims submitted under deleted codes will be denied automatically, creating an immediate revenue gap. Billing staff unfamiliar with E/M-level documentation for maternity visits will underdocument encounters, leading to downcoded reimbursements. Practices caught between payers on different code sets will spend additional hours on rework, appeals, and manual verification. And the 1 to 2 percent reimbursement decrease from the conversion factor expiration means the margin for billing errors is even thinner than it was in 2026.

The most common issue we see providers run into during coding transitions is assuming the new codes work the same way as the old ones. They do not. Under the current global package, a single CPT code covers an entire maternity episode. Under the new system, every encounter is a distinct billable event with its own documentation, coding, and modifier requirements. The shift in workflow is fundamental, not incremental.

In-House Billing vs. an OB/GYN Billing Partner

The 2027 transition raises a practical question for every OB/GYN practice: can your current billing setup handle this? If your billing is managed by one or two staff members who learned on global obstetric codes and have never billed maternity care on a per-visit basis, the transition is a significant operational lift. If you are still evaluating options, our guide on how to find the right OB/GYN medical billing service covers the key factors to weigh when comparing billing partners.

A billing company with direct OB/GYN experience already understands the documentation differences between global and unbundled maternity billing, manages modifier TH compliance across multiple payers, and has the volume to test workflows with major insurers before the transition date. They can also absorb the dual-code-set complexity if the G-codes are finalized, because they are already handling maternity claims across different payer rule sets.

Providers often come to us after a coding change has already caused problems, not before. The practices that come through the transition cleanly are the ones that evaluate their billing partner’s readiness now, while there is still time to test and adjust. OB/GYN Bill Co connects practices with billing companies that specialize in obstetric and gynecological claims, not generalists who will treat a maternity transition like a routine fee schedule update.

Frequently Asked Questions

Next Steps

Review the ACOG transition timeline and modifier TH guidance at acog.org before your September 1 billing cycle.

If you are currently managing global obstetric billing in-house, learn more about how the global package works and what is changing in our CPT code 59400 overview.

Practices dealing with high-risk pregnancy claims during the transition should review our guide to OB/GYN billing for high-risk pregnancies for modifier and documentation specifics.

When you are ready to evaluate whether your billing partner can handle the 2027 restructure, we can connect you with an OB/GYN-specialized billing company in as little as 30 minutes.