Summary: Background: Global rollout of dolutegravir-based antiretroviral therapy (ART) has been hampered in part by insufficient safety data in pregnancy. We compared birth outcomes among women initiating dolutegravir-based ART with those among women initiating efavirenz-based ART in pregnancy in Botswana. Methods: In this observational study, we captured birth outcome data at eight government hospitals throughout Botswana (~45% of all deliveries in the country) in an ongoing study that started on Aug 15, 2014. In 2016, Botswana changed first-line ART from efavirenz-tenofovir-emtricitabine to dolutegravir-tenofovir-emtricitabine, including for pregnant women. This analysis includes women starting either efavirenz-based ART or dolutegravir-based ART during singleton pregnancy (regimen started and delivery occurring between Aug 15, 2014, and Aug 15, 2016, for efavirenz-based ART and between Nov 1, 2016, and Sept 30, 2017, for dolutegravir-based ART). We excluded births to mothers who had switched regimen or stopped ART. The primary outcomes were the combined endpoints of any adverse outcome (stillbirth, preterm birth [