BACKGROUND: Adolescent girls living in low-income urban informal settlements face unique challenges that elevate their susceptibility to early childbearing. However, there has been limited research attention, especially qualitative studies, on their use or non-use of antenatal care (ANC) services. Informed by the socioecological theory, we examined the obstacles to and facilitators of ANC services use among pregnant adolescent girls in a low-income urban informal settlement in Kenya. METHODS: The study adopted a qualitative explanatory design. We purposively selected 22 adolescent girls aged 13-19 who were either pregnant or had given birth, 10 parents and three health providers to participate in individual interviews. We employed inductive and deductive thematic analyses informed by socioecological theory to explain the barriers to enablers of antenatal services use among pregnant adolescent girls in low-income informal settlements. FINDINGS: Most adolescent girls interviewed faced barriers at multiple socioecological levels, resulting in delayed ANC initiation and fragmented engagement with services. At the intrapersonal level, girls grappled with internalised stigma and late pregnancy recognition and acceptance, often dismissing early signs due to fear or denial. Their young age and limited knowledge of maternal health left them terrified in fear, caught between societal judgement and the daunting prospect of confronting their condition. At the interpersonal level, societal stigma and discrimination pushed many into secrecy, hindering their access to antenatal services. However, parents, other family members, and health providers played a key role in enabling access to care by offering various forms of support to pregnant girls, including offering counselling and accompanying girls to clinics. At the organisational level, user fees and condescending health providers' attitudes hindered ANC use. Yet, good patient-provider communication, privacy and confidentiality played a key role in enabling ANC attendance. CONCLUSION: Pregnant adolescent girls face unique challenges that prevent them from accessing ANC early and completing the recommended number of visits. These challenges range from intrapersonal factors to interpersonal and organisational factors. Programmes to improve early initiation of ANC for pregnant adolescents should include interventions that address the social stigma associated with early and unintended pregnancy, promote family support and make health facilities responsive to the needs of pregnant girls.