25% of Medicare-enrolled obstetrician-gynecologists were in groups with five or fewer obstetrician-gynecologists in 2024, down from 31% in 2019
Published Jul 2026 · CMS Doctors and Clinicians group rosters and Part B provider types📋 CiteSee the data →
Medicare-enrolled obstetrician-gynecologists by the size of their largest group · 2019–2024
Each clinician is counted once, in the group with the most obstetrician-gynecologists on its roster that year. Bands count obstetrician-gynecologists. Full method below.
Over the same years, the share in organizations of 500 or more physicians rose from 18% to 26%.
The bands. Each year's roster is read on its own and sorted into four bands by the number of obstetrician-gynecologists in the clinician's largest group: five or fewer, 6 to 19, 20 to 49, and 50 or more.
Ownership. Rosters cannot see ownership. A practice owned by a larger company that keeps its own Medicare billing number still counts here as a small group, so a small change does not mean a specialty stayed independent.
A record of group size, not a verdict on whether larger groups are better or worse for patients, prices, or clinicians.
What this is
The share of Medicare-enrolled obstetrician-gynecologists on rosters of each group size, 2019 to 2024.
What it is not
Not a count of acquisitions or mergers, not ownership or employment, and not who bills what. A roster records enrollment, not activity, and cannot show why a group grew.
› How this is counted
Each clinician's specialty is their most frequent Part B provider type across 2020 to 2024, so the 2019 base counts only clinicians who billed in 2020 or later, and clinicians who billed too little Part B to carry a label are not counted. The specialty is Obstetrics & Gynecology. Years after 2024 are not included because they are not on the same basis. Each clinician is counted once a year, in the group with the most obstetrician-gynecologists on its roster, and a group that re-registers can appear as a new group. Where a second figure is printed, it counts physicians only, because nurse-practitioner and physician-assistant roster growth moves a count of every clinician. Medicare's 2019 roster snapshot lists fewer clinicians than later years' do, so part of the change since 2019 may reflect a fuller list rather than a shift in group size.