Semen analysis
Each man provided a semen sample by masturbation in a room close to
the laboratory. The ejaculation abstinence period prior to sampling was
recorded. The sample was collected in a plastic container and kept at
378C until analysis. Semen volume was estimated by weighing the collection
tube, and the percentage of motile spermatozoa was determined.
Sperm concentration was assessed using a Bu¨rker-Tu¨rk haemocytometer,
and sperm morphology was assessed according to strict criteria. Morphology
slides were assessed for only 1897 men (54.4%) due to lack of
resources, however, the slides were randomly selected. Total sperm
count was calculated as semen volume × sperm concentration. Details
of the methods have previously been described (Jørgensen et al.,
1997, 2002).