This study had the purpose of identifying personal, family and social determinants that can intervene in the pregnancy of teenagers of the city of San Francisco del Rincón, Gto. (Mexico). It was a field study, with a traverse, comparative and correlating design. Qualitative interviews were carried out in order to obtain data (personal, family and pregnancy history). Sample: 61 teenagers; 30 in type group (pregnant) and 31 in the control group (not pregnant). Results. – In the Control group every girl is single, in the type group everybody lives in couple arrangement. About one half of the control group studies (10% in the standard group). Teenagers working: control 26%, type 10%. Stopped studying in childhood: type 85%, control 39%. Type group: reports of worse abuse, labor activities and sadness during childhood; lower education level, worse relationship with the family. More than 90% stated that their first pregnancy was wanted and planned by them and their couples; little more than 50% stated that they would have liked to wait longer to be pregnant the first time.