Fetal outcome among pregnancies in natural family planning acceptors: An international cohort study
Simpson, Joe Leigh; Gray, Ronald H.; Queenan, John T.; Kambic, Robert T.; Pérez, Alfredo; Mena, Patricio; Barbato, Michele; Pardo, Francisco; Tagliabue, Guillermo; Bitto, Adenike; Stevenson, Wilma (1991)