Timing of puberty in relation to semen characteristics, testicular volume, and reproductive hormones: a cohort study

Abstract

To investigate if timing of puberty is associated with semen characteristics, testicular volume, and reproductive hormone levels. Cohort study. The Danish National Birth Cohort (DNBC) and its sub-cohort, the Fetal Programming of Semen Quality (FEPOS) cohort of 1,058 young men. Self-reported information on timing (younger, same age, older than peers) of the pubertal markers: voice break (primary exposure), pubic hair growth, regular shaving, and axillary hair growth. We estimated the relative differences with 95% confidence intervals (CI) for semen characteristics (semen volume, sperm concentration, total sperm count, sperm motility, percentage of morphologically normal spermatozoa), testicular volume, and reproductive hormones (follicle stimulating hormone [FSH], luteinizing hormone [LH], sex hormone-binding globulin [SHBG], testosterone, estradiol, free androgen index [FAI]) obtained at a median age of 19.2 years according to timing of pubertal development. Compared to men reporting voice break 'same age as peers', men reporting voice break 'older than peers' tended to have lower total sperm count (-12% [-25%, 4%]) and lower percent morphologically normal spermatozoa (-10% [-20%, 2%]), whereas men reporting voice break 'younger than peers' tended to have lower proportion of non-progressive and immotile spermatozoa (-6% [-13%, 1%]) and larger testicular volume (7% [1%, 13%]). The pattern was less consistent for the other pubertal markers.For reproductive hormones, voice break 'older than peers' tended to have higher FSH (24% [-1%, 55%]), higher SHBG (7% [0%, 15%]), lower estradiol (-14% [-23%, -5%]) and lower FAI (-8% [-14%, -1%]), whereas voice break 'younger than peers' tended to have higher LH (4% [-2%, 11%]), higher testosterone (5% [0%, 11%]), higher estradiol (17% [6%, 29%]) and higher FAI (4% [-2%, 11%]). When the categorical pubertal markers were analyzed as a linear term to assess for dose-dependency, older age at pubertal development were associated with higher FSH, higher SHBG, lower testosterone, lower estradiol and lower FAI for most pubertal markers. These results lend weak support to the hypothesis that older age at pubertal development is associated with markers of reduced male fecundity, especially reproductive hormone levels, although associations with semen characteristics and testicular volume were statistically insignificant.