BACKGROUND: West Africa has the highest proportion of married adolescents, and the highest adolescent childbirth rate and maternal death rate in sub-Saharan Africa. However, few studies have focused on the type and quality of health care accessed by pregnant young women in countries in this subregion. METHODS: We obtained data from Demographic and Health Surveys done between 2010 and 2014, to compare the use, timing, source, and components of antenatal care between adolescent and older first-time mothers in 13 west African countries. The sample included primiparous women who were aged 15-49 years with a livebirth in the 5-year survey recall period, and women were assigned to one of three groups on the basis of age at the time of childbirth: adolescent (10-19 years), young adults (20-24 years), or adults (25 years or older). We calculated the percentage of women who: attended at least one antenatal care visit, completed at least one visit during the first trimester of pregnancy, attended four or more appointments in antenatal care, and received four components of antenatal care (blood pressure measurement, urine tests, blood tests, and information on complications), as well as the sector where the women received care. We primarily report the comparison between adolescents and young adults. FINDINGS: In 2016, we acquired data from the Demographic Health Surveys from 13 west African countries between 2010 and 2014 on primiparous women. The study sample was 19 211 women, of whom 10 025 (52%) were adolescents, 6099 (32%) were young adults, and 3087 (16%) were adults. Overall, 17 386 (91%) of 19 211 first-time mothers made use of antenatal care facilities on at least one occasion. 3597 (41%) of 8741 adolescents compared with 8202 (47%) of all 17 386 women began the use of antenatal care during the first trimester. Across west Africa, 5430 (62%) of 8741 adolescents had four or more antenatal care visits compared with 4067 (71%) of 5717 young adults and 2358 (81%) of 2928 adults. Of those who had four or more visits to antenatal care, 2779 (51%) of 5430 adolescents received all the antenatal care components examined compared with 2488 (61%) of 4067 young adults and 1600 (68%) of 2358 adults. Although most women received antenatal care in the public sector, in nine of the 13 countries, the proportion of women that used the private sector was higher in older mothers. INTERPRETATION: Although a large percentage of west African adolescents use some antenatal care for their first birth, they seek care later, make fewer visits during pregnancy, and receive fewer components of care than older first-time mothers. Governments must ensure the pregnancy care accessed by adolescent mothers is of high quality and tailored to meet their needs. FUNDING: MSD for Mothers.