title: Factors associated with male infertility: a case-control study of 218 infertile and 240 fertile men.
abstract: OBJECTIVE
  To determine the likely risk factors, such as smoking and drinking habits, and occupational groups, for infertility in a group of infertile men with no known cause, compared with a group of fertile men; and to examine the effects of the semen parameters, such as volume, density, motility, viability and normal morphology, on fertility.
  
  
  METHODS
  A case-control study.
  
  
  METHODS
  The department of obstetric and gynaecology of a tertiary general hospital.
  
  
  METHODS
  Six hundred and forty consecutive male partners of couples trying to conceive were recruited from an infertility clinic. Of these, the cases comprised 218 men who had no known cause for their infertility. Two hundred and forty men whose wives were pregnant at the time of the study were recruited as controls.
  
  
  RESULTS
  The semen parameters (e.g. density, total sperm counts, motility, viability and normal morphology) of all cases were significantly poorer than that of the controls. The risk of infertility is associated with smoking (crude OR 2 x 82, 95% CI 1 x 93-4 x 13; adjusted OR 2 x 96; 95% CI 1 x 98-4 x 42). Technicians (adjusted OR 2 x 81; 95% CI 1 x 51-4 x 24) and professional, senior officials and managers were also at a greater risk of infertility (adjusted OR 2 x 36; 95% CI 1 x 26-4 x 40), compared with service and clerical workers. The significant factors predicting infertility were smoking, density of sperm, and viability of sperm. Smoking increased the odds of being infertile. Higher sperm counts and larger percentage of viable sperm decrease the odds of infertility. Based on the multiple logistic regression model, the odds ratio for infertility = (94 x 70) x (2 x 88(smoking)) X (0 x 29(logdensity)) X (0 x 95(viability)).
  
  
  CONCLUSIONS
  Smoking, density of sperm and the viability of sperm are significant predictors for infertility among men.
authors.affiliation: Department of Community, Occupational and Family Medicine, National University of Singapore, Republic of Singapore.
authors.forename: S E
authors.initials: SE
authors.lastname: Chia
authors.forename: S T
authors.initials: ST
authors.lastname: Lim
authors.forename: S K
authors.initials: SK
authors.lastname: Tay
authors.forename: S T
authors.initials: ST
authors.lastname: Lim
mesh_terms: D000328:Adult; D000428:Alcohol Drinking / Q000009:adverse effects*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007248:Infertility, Male / Q000209:etiology*; D008297:Male; D009784:Occupational Diseases / Q000209:etiology*; D011247:Pregnancy; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D013076:Sperm Count; D013081:Sperm Motility