IMPORTANCE: Since 1994, the US Department of Health and Human Services has published treatment guidelines for pregnant women living with HIV. Understanding how well prescribing patterns correspond with treatment guidelines could inform health policy and influence future clinical practice. OBJECTIVES: To compare antiretroviral prescribing practices over time among pregnant women living with HIV with Department of Health and Human Services treatment guidelines and identify factors associated with receiving recommended regimens. DESIGN, SETTING, AND PARTICIPANTS: A prospective cohort study of 1582 pregnant women living with HIV were enrolled in the Pediatric HIV/AIDS Cohort Study Surveillance Monitoring of ART (antiretroviral therapy) Toxicities study between January 1, 2008, and June 30, 2017. The study was conducted at 18 academic research hospitals in the United States. EXPOSURES: Antiretroviral medications (ARVs) prescribed during pregnancy. MAIN OUTCOMES AND MEASURES: Proportion of regimens prescribed to pregnant women living with HIV qualifying as preferred or alternative according to Department of Health and Human Services guidelines, stratified by timing of initiation. RESULTS: Of 1867 pregnancies (among 1582 pregnant women living with HIV with a mean [SD] age of 28.6 [6.1] years at conception), 1264 (67.7%) occurred among women self-identified as black, 480 (25.7%) self-identified as white, and 123 (6.6%) self-identified as other or unreported race/ethnicity. Antiretroviral medications were initiated prior to conception for 790 women (42.3%), resumed during pregnancy for 625 women (33.5%), and initiated during pregnancy for 452 women (24.2%). Only 925 pregnancies (49.5%) were associated with prescribed ARVs designated as preferred or alternative, while 492 (26.4%) involved ARVs with insufficient evidence for use during pregnancy and 136 (7.3%) involved ARVs that were not recommended during pregnancy. A higher proportion of treatment-naive pregnant women initiating ARVs were prescribed preferred or alternative ARVs compared with those resuming ARVs or those treated with ARVs before conception (316 of 452 [69.9%] vs 325 of 625 [52.0%] vs 284 of 790 [35.9%]; P < .001). A total of 91 of 452 women (20.1%) initiating ARVs during pregnancy were prescribed ARVs with insufficient evidence for use during pregnancy or not recommended during pregnancy. Among women resuming ARVs, those with a viral load greater than 1000 copies/mL early in pregnancy had higher odds of being prescribed guideline-recommended ARVs (adjusted odds ratio, 2.03 [95% CI, 1.33-3.10]) compared with those with a viral load of 400 copies/mL or less. CONCLUSIONS AND RELEVANCE: This study suggests that US ARV prescribing practices for pregnant women living with HIV do not align well with national guidelines. This finding is particularly concerning when treatment is initiated during pregnancy. Further research is needed to understand disparities between prescribing practices and evidence-based guideline recommendations.