1. United Nations Population Division. Estimates and Projections of Family Planning Indicators 2020: Regions (UN, 2020).
2. Moreau, C., Cleland, K. & Trussell, J. Contraception 76, 267–272 (2007).
3. Trussell, J., Aiken, A. R. A., Micks, E. & Guthrie, K. A. in Contraceptive Technology 21st edn (eds Hatcher, R. A. et al.) (Ayer, 2018).
4. Ali, M. M., Cleland, J. G., Shah, I. H. & World Health Organization. Causes and Consequences of Contraceptive Discontinuation (WHO, 2012).
5. Bearak, J., Popinchalk, A., Alkema, L. & Sedgh, G. Lancet Glob. Health 6, e380–e389 (2018).