PROJECT SUMMARY/ABSTRACT Adolescence and young adulthood are periods of high vulnerability to HIV and unintended pregnancies for young women in South Africa. Adolescent girls and young women (AGYW) aged 15 to 24 comprise 25% of new HIV infections in South Africa. Additionally, 18% of AGYW give birth by age 18. HIV risk increases significantly during pregnancy and postpartum, highlighting the need for efficacious HIV prevention strategies for this population. The World Health Organization guidelines recommend that women continue using PrEP if they become pregnant and remain at risk for HIV. However, South Africa has not yet implemented these recommendations into its national PrEP guidelines. This 2-year diversity supplement seeks to build the evidence base on PrEP use among pregnant AGYW and aligns with NICHD's Strategic Plan, Setting the Foundation for Healthy Pregnancies and Lifelong Wellness under the cross-cutting topics of infectious disease and global health. The Specific Aims are: Aim 1: Compare pregnancy outcomes (e.g., termination, miscarriage) and birth outcomes (e.g., gestational age, birth weight, birth length, fetal head circumference) between pregnant AGYW who uptake PrEP and those who do not. Aim 2: Examine the association between pregnancy and PrEP adherence and persistence among AGYW. Aim 3: Use journey mapping to examine and depict pregnant AGYW's experience using PrEP. Aim 4: Qualitatively explore provider attitudes and beliefs toward AGYW who are pregnant and use PrEP and providers clinical recommendations regarding PrEP use during pregnancy. Throughout the supplement period, the proposed candidate will engage in a variety of research and professional development activities, including participating in didactic trainings, continuing to produce scholarly research, and applying for additional National Institute of Health (NIH) funding. The activities comprising this supplement will provide the candidate with opportunities to enhance the necessary skills to become an independent NIH-funded researcher. Preliminary study data will be applied to a future NIH R21 proposal to develop an intervention to improve PrEP adherence and persistence among pregnant and postpartum AGYW in South Africa.