Barriers to antiretroviral therapy (ART) adherence among pregnant women are varied and complex. This study explored the constructs of a theoretical model, the Health Belief Model (HBM) to understand and predict ART adherence among pregnant women in Guyana. A cross-sectional study surveyed 108 pregnant women attending 11 primary care clinics. ART adherence ranging from the past weekend to three months was assessed through self-reports, and health beliefs with the Adherence Determinants Questionnaire (ADQ). Constructs with sufficient variation in responses were tested for association with the level of adherence using Spearman’s rank correlation coefficient and test. Sixty-seven per cent (72) of the women reported being always adherent. Although there was positive endorsement of ART treatment and adherence, the HBM did not help in understanding or predicting ART adherence in this population. Only one item from the perceived susceptibility construct was significantly associated (p = 0.009) with adherence. Interventions are warranted to address ART adherence in this population, as 19% of the women were recently non-adherent. Although the ADQ did not contribute to a deeper understanding or provide insight into pathways that can be targeted for intervention, theoretical models can play a key role in identifying these pathways.