Authors Hart RJ, Doherty DA, McLachlan RI, Walls ML, Keelan JA, Dickinson JE, Skakkebaek NE, Norman RJ, Handelsman DJ
Review Date November 2015
Citation Human Reproduction 2015; 30(12): 2713–2724
The testes have two functions, spermatogenesis and steroidogenesis. Valid population-based reference ranges are needed to accurately assess testis function. Although reference ranges for testosterone are considered to have reasonable validity, those for spermatogenesis are more likely to be biased, mainly due to the need for men to provide semen samples and the use of potentially biased populations such as fertility clinics, with most having low recruitment rates. Studies have suggested there may be a high proportion of young men with semen variables that do not meet all the WHO reference range criteria for fertile men. However, the concerns about the validity of reference ranges make it difficult to examine claims that sperm production in the general population may be declining.
To use information from an Australian birth cohort of men (now ~20 years old) with a high ongoing participation rate, i.e. a relatively unbiased population, to examine the parameters and influences on testicular function.
The Western Australian Pregnancy Cohort (Raine) was established in 1989. At 20–22 years of age, men were contacted to attend for a general follow-up, with 753 participating out of the 913 contactable men. Of these, 423 men (56% of participants in the 20–22 years cohort, 46% of contactable men) participated in a testicular function study. Of the 423 men, 404 had a testicular ultrasound, 365 provided at least one semen sample, 287 provided a second semen sample and 384 provided a blood sample.
Testicular ultrasound was used to measure testicular volume and presence of epididymal cysts and varicoceles. Standard semen assessments were done as well as sperm chromatin structural assay (SCSA). Serum blood samples were analysed for serum luteinizing hormone (LH), follicular stimulating hormone (FSH), inhibin B, testosterone, dihydrotestosterone (DHT), dehydroepiandrosterone (DHEA), estradiol, estrone and the primary metabolites of DHT.
Men who participated in this study (n=423) were not significantly different to men who did not participate (n=282) with respect to BMI, age, weight, smoking and circulating reproductive hormones but were taller and had higher alcohol intake.
Cryptorchidism (note, only 9 men had this condition) was associated with a significant reduction in testis (P = 0.047) and semen (P = 0.027) volume, sperm concentration (P = 0.007) and output (P = 0.003), but not with other semen variables or reproductive hormones.
Varicocele was associated with smaller testis volume (P < 0.001), lower sperm concentration (P = 0.012) and output (P = 0.030) and lower serum inhibin B levels (P = 0.046).
Smoking, alcohol intake, herniorrhaphy, an epididymal cyst, medication and illicit drugs were not significantly associated with any semen variables, testicular volume or circulating reproductive hormones. BMI had a significantly negative correlation with semen volume (r = -0.12, P = 0.048), sperm output (r = -0.13, P = 0.02), serum LH (r = -0.16, P = 0.002), inhibin B (r = -0.16, P < 0.001), testosterone (r = -0.23, P < 0.001) and DHT (r = -0.22, P < 0.001) and a positive correlation with 3aD metabolite (r = 0.13, P = 0.041) and DHEA (r = 0.11, P = 0.03).
Testis volume was significantly positively correlated with sperm concentration (r = 0.25, P < 0.001) and output (r = 0.29, P < 0.001) and inhibin B (r = 0.42, P < 0.001), and negatively correlated with serum LH (r = -0.24, P < 0.001) and FSH (r = -0.32, P < 0.001). SCSA was inversely correlated with sperm motility (r = -0.20, P < 0.001) and morphology (r = -0.16, P = 0.005).
WHO semen reference criteria were all met by only 52 men (14.4%). Some criteria were not met at first analysis in 15–20% of men, including semen volume (< 1.5 ml, 14.8%), total sperm output (< 39 million, 18.9%), sperm concentration (< 15 million/ml, 17.5%), progressive motility (< 32%, 14.4%) and morphologically normal sperm (< 4%, 26.4%), while all five WHO criteria were not met in four participants (1.1%).
This study demonstrated the feasibility of establishing a birth cohort to provide a relatively unbiased insight into population-representative sperm output and function and of investigating its determinants from common exposures. In keeping with previous reports, varicocele and cryptorchidism were associated with spermatogenesis, and obesity with sperm output and reproductive hormones. However, alcohol, smoking and other drug consumption and the presence of epididymal cysts were not associated with testicular function in this population.
Points to Note
- This birth cohort study provides data on testicular function in a relatively unbiased population of Australian young men.
- The data confirm previously known factors that adversely affect reproductive function such as varicocele, cryptorchidism and obesity but did not support the effects of other exposures such as drugs and cigarette smoking. There is also potential to examine other environmental exposures in the future.
- The results suggest that for large studies, a single semen sample may be adequate, albeit with sample size implications due to high variability, while for individual fertility assessments multiple semen assessments are desirable.
- Although the population used in the study is from an unselected birth cohort, the response rate of 56% in the testicular function study suggests possible residual participation bias.
- A relatively high proportion of the young men had semen variables that did not meet the WHO reference criteria, as has been shown previously. This is likely due to the WHO reference ranges being based on populations of recently fertile men. In Australia, recent fathers represent only ~5% of men of reproductive age.