Objective To describe antiretroviral therapy (ART) regimens during pregnancy among women living with HIV (WLWH) in Denmark and to examine the association between ART use in pregnancy and adverse birth outcomes. Methods A population-based cohort study including all pregnancies among WLWH in Denmark between 2000 and 2019. Data were collected through national registries. Temporal trends of ART use in pregnancy were evaluated. Logistic regression models were used to examine the association of ART use in pregnancy and other risk factors with adverse birth outcomes. Results In total, 589 pregnancies were included. Combination treatment with a nucleoside reverse transcriptase inhibitor (NRTI) and a protease inhibitor (PI) was the most common ART regimen (96%). ART regimen, PI use in pregnancy and timing of ART initiation were not significantly associated with increased odds of preterm birth, small for gestational age or low birth weight. First-trimester initiation of ART was significantly associated with increased odds of intrauterine growth restriction in the multivariate analysis [adjusted odds ratio (aOR) = 3.78, 95% confidence interval (CI): 1.23-11.59], while first trimester PI use was associated with increased odds of IUGR in the univariate analysis only [OR = 3.24, 95% CI: 1.13-9.30]. Smoking, comorbidity, and maternal HIV RNA >= 50 copies/mL were independently associated with increased odds of adverse birth outcomes. Conclusions Pregnant WLWH living in Denmark are generally well treated with HIV RNA < 50 copies/mL at delivery and NRTI + PI as the most common ART regimen used in pregnancy. Initiation of ART in the first trimester may be associated with poor fetal growth. The association between ART use in pregnancy and adverse birth outcomes may partly be explained by maternal risk factors.