Adolescent pregnancy rates are high worldwide. However, insufficient information exists regarding the frequency of birth control methods used before the first pregnancy and postpartum. In the current study, we analyzed the association of sociodemographic factors with the knowledge of birth control methods and their use before and after pregnancy in a sample of adolescents in Mexico City. A cohort study was conducted on 600 pregnant adolescents in Mexico City, from 2013 to 2017, at a health care institution providing prenatal care. Participants were assessed during the second trimester and four months postpartum. The questionnaire explored the knowledge of birth control methods, their use, and other associated factors. Two logistic regression models were implemented to identify potential variables associated with the lack of birth control method use before and after pregnancy. The mean age of participants was 15.4 + 1 years, of which, 48% and 65.2% used a birth control method before pregnancy and postpartum, respectively. We found that the main factors associated with increased risk of not using any birth control method before pregnancy included being under the age of 15 years, school dropout, having an educational lag, initiation of sexual life before the age of 15, and having a mother who did not inform their child about contraceptives. By contrast, variables associated with a higher risk of not using any contraceptive methods after pregnancy included educational lag, lower level of education, and the fact that the adolescent had not used any birth control prior to the pregnancy.