Semen analysis in fertile patients undergoing vasectomy: reference values and variations according to age, length of sexual abstinence, seasonality, smoking habits and caffeine intake - Sobreiro, Bernardo Passos; Lucon, Antonio Marmo; Pasqualotto, Fábio Firmbach; Hallak, Jorge; Athayde, Kelly silveira; Arap, Sami (São Paulo Medical Journal, 2005)