DYnamics of Contraception in Eswatini (DYCE): protocol for a high-frequency, longitudinal cell phone survey.

Introduction: By 2030, an estimated 42% of the world's adolescent girls and young women (AGYW) will live in sub-Saharan Africa (SSA), where a quarter of AGYW pregnancies are undesired and AGYW represent 75% of new HIV infections. Most AGYW in SSA use short-acting contraceptive methods, including many who rely solely on condoms, which results in variable patterns of protection against undesired pregnancies and HIV. Dynamics of contraceptive use and HIV prevention efforts are poorly understood but the DYnamics of Contraception in Eswatini study will contribute to the understanding of the complex relationship between sexual behaviours, risk perception and HIV and pregnancy prevention.