Objectives: To describe gender and geographical inequalities in invitations to review and the response to these invitations and to assess whether inequalities increased during the covid-19 pandemic.

Design: Retrospective cohort study.

Setting: 19 specialist medical journals and two large general medical journals from BMJ Publishing Group.

Population: Reviewers invited to review manuscripts submitted between 1 January 2018 and 31 May 2021. The cohort was followed up to 28 February 2022.

Main outcome measures: Reviewer's agreement to review.

Results: A total of 257 025 reviewers were invited (38.6% (88 454/228 869) women), and 90 467 (35.2%) agreed to review. Invited reviewers were mainly (217 682; 84.7%) affiliated with high income countries: Europe (122 414; 47.6%), North America (66 931; 26.0%), Africa (25 735; 10.0%), Asia (22 693; 8.8%), Oceania (16 175; 6.3%), and South America (3076; 1.2%). Independent factors associated with agreement to review were gender (odds ratio 0.89, 95% confidence interval 0.87 to 0.92, for women compared with men), geographical affiliation (2.89, 2.73 to 3.06, for Asia; 3.32, 2.94 to 3.75 for South America; 1.35, 1.27 to 1.43, for Oceania; and 0.35, 0.33 to 0.37, for Africa compared with Europe), and country income (0.47, 0.45 to 0.49, for upper middle income; 5.12, 4.67 to 5.61, for lower middle income; and 4.66, 3.79 to 5.73, for low income compared with high income country). Agreement was also independently associated with editor's gender (0.96, 0.93 to 0.99, for women compared with men), last author's geographical affiliation (0.80, 0.78 to 0.83, for Asia; 0.89, 0.85 to 0.94, for Oceania compared with Europe), impact factor (1.78, 1.27 to 2.50, for >10 compared with <5), and type of peer review process (0.52, 0.35 to 0.77, for open compared with anonymised). During the first and second phases of the pandemic, agreement was lower than in the pre-pandemic period (P<0.001). The interaction between time periods and covid-19 related topic and reviewer's gender was non-significant. However, significant interaction was found between time periods and covid-19 related topic and reviewer's geographical affiliation.

Conclusions: To reduce bias and improve diversity, editors need to identify and implement effective strategies and continually evaluate progress against these to ensure that more women and researchers from upper middle income and low income countries are involved in review.