Diurnal variation of semen quality in human males

The possibility of a diurnal variation in semen quality was tested in 54 hu man males attending our infertility clinic. Of the enrolled subjects, 24 we re normozoospermic and 30 were suffering from oligo- and/or asthenozoosperm ia, Seminal fluid was collected by masturbation twice by each subject, once in the morning (7:00-7:30 a.m.) and once in the afternoon (5:00-5:30 p.m.) . Abstinence from sexual intercourse for 3-4 days before each of the two co llections was requested. Semen parameters were evaluated independently by t wo biologists before and after pellet swim-up. Beside similar macroscopic p arameters, specimens collected in the afternoon showed a higher number (P < 0.01) and concentration (P < 0.01) of spermatozoa, Also, immediately (P < 0.05), and at 1 h (P < 0.02) and 2 h (P < 0.01) after pellet swim-up, the n umber of spermatozoa with progressive linear motility was higher in the aft ernoon than in the morning. These data are the first documenting a diurnal rhythm in sperm quality which may contribute to the reported variability in semen parameters, and may prove useful for spontaneous and assisted concep tions.