Annual variation in semen characteristics and plasma hormone levels in men undergoing vasectomy.

Prevasectomy levels of plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T), estradiol (E2), and 20 alpha-dihydroprogesterone (20 alpha-DHP), as well as semen analyses including semen volume, sperm count, and sperm motility from 260 healthy men were evaluated for annual changes. A statistically significant (P less than or equal to 0.015) high-amplitude seasonal variation with the peak in April to May was detected in semen volume, sperm count, and sperm motility. A statistically significant (P less than or equal to 0.04) annual change of moderate T to large FSH amplitude was detected in each of the five plasma endocrine variables as well. Plasma LH, T, and E2 peaked in autumn, while FSH and 20 alpha-DHP peaked in summer. Analysis of postvasectomy LH, FSH, E2, 20 alpha-DHP, and T blood levels for the 3 years following vasectomy revealed loss of seasonal rhythmicity as a group phenomenon in LH, E2, and T. The amplitude of the seasonal variation in FSH was decreased and that in 20 alpha-DHP was unchanged compared with before-vasectomy baselines. For those annual rhythms which persisted following vasectomy, the peak time was unchanged. Compared with the prevasectomy group annual mean, that for each of the endocrine values was unchanged, except for that of LH and T, which was slightly, yet statistically significantly, elevated. The existence of prominent annual variation implicates their consideration in the design of research protocols involving investigation of reproductive phenomena in human beings.