BackgroundAntenatal care (ANC) clinics remain important entry points to HIV care for pregnant women living with HIV—including adolescents. Prior knowledge of their HIV status at ANC enrollment is crucial to providing services for prevention of mother-to-child transmission (PMTCT) of HIV. We examined known HIV status of pregnant adolescents and women in other age groups at ANC enrollment.MethodsA descriptive study of routinely reported PMTCT data from 419 facilities in Eswatini, Ethiopia, and Mozambique, from January through December 2018 was conducted. We assessed knowledge of HIV status by country for three age groups: adolescents aged 15–19 years, young women aged 20–24 years, and older women aged 25–49 years. We report HIV prevalence and proportions of known and newly diagnosed HIV infections in women, by age group and country. The data were summarized by frequencies and proportions, including their 95% confidence intervals.ResultsAmong the facilities examined, 52 (12.4%) were in Eswatini, 63 (15.0%) in Ethiopia, and 304 (72.6%) in Mozambique. Across three countries, 488,121 women attended a first ANC visit and 23,917 (4.9%) were HIV-positive. Adolescents constituted 22% of all ANC attendees, whereas young and older women represented 33% and 45%, respectively. HIV prevalence was lowest among adolescents than in other age groups in Eswatini (adolescents 11.9%, young 24.2% and older 47.3%), but comparable to young women in Ethiopia (adolescents 1.6%, young 1.6% and older 2.2%) and Mozambique (adolescents 2.5%, young 2.5% and older 5.8%), However, in each of the three countries, lower proportions of adolescents knew their HIV-positive status before ANC enrollment compared to other age groups: in Eswatini (adolescents 51.3%, young 59.9% and older 79.2%), in Ethiopia (adolescents 42.9%, young 63.7% and older 75.2%), and in Mozambique (adolescents 16.4%, young 33.2% and older 45.6%).ConclusionOverall, adolescents made up nearly one-quarter of the women examined and had the least knowledge of their HIV status at ANC enrollment. Their HIV prevalence and known HIV-positive status varied widely across the countries examined. Adolescent-friendly sexual and reproductive health, and PMTCT services, before pregnancy, are needed to improve knowledge of HIV status and support pregnant adolescents and their infants.Plain English summaryAntenatal care (ANC) clinics are important for HIV testing of pregnant adolescents, who may not know their HIV-positive status at the first ANC visit. We describe data on pregnant adolescents and women in other age groups in ANC services to examine their prior HIV status at ANC enrollment across three African countries.We examined data from 419 PMTCT sites in Eswatini, Ethiopia, and Mozambique from January-December 2018, to evaluate HIV testing results for adolescents, young and older women aged 15–19, 20–24 and 25–49 years, respectively. We report the number of women living with HIV and the proportions of known and newly identified women living with HIV, by age-group and country.Across three countries, 488,121 women attended ANC and 23,917 (4.9%) were living with HIV. Adolescents constituted 22% of all ANC attendees, whereas young and older women represented 33% and 45%, respectively. HIV prevalence in each country compared to other age groups was lowest and varied among adolescents from 11.9% in Eswatini, to 1.6% in Ethiopia and to 2.5% in Mozambique. Also, fewer adolescents knew their HIV-positive status before ANC enrollment compared to young and older women from 51.3% in Eswatini, 42.9% in Ethiopia to only 16.4% in Mozambique.Pregnant adolescents made up nearly one-quarter of all ANC attendees; a majority of them had no previously known HIV-positive status. Adolescent-friendly, sexual and reproductive health services, before pregnancy and in PMTCT services, are needed to support pregnant adolescents and their infants.