Evaluating an external quality assurance program for semen analysis in China during 2009-2020

Association between central obesity and semen quality: A cross-sectional study in 4513 Chinese sperm donation volunteers

BACKGROUND

General obesity classified by body mass index has been linked to a reduction in semen quality; however, evidence on the adverse effect of central obesity on semen quality remains limited.

OBJECTIVES

To investigate the association between central obesity and semen quality.

MATERIALS AND METHODS

We conducted a cross-sectional study of 4513 sperm donation volunteers in Guangdong Provincial Human Sperm Bank during 2018-2021. Three central obesity indicators, including waist circumference, waist-to-hip ratio, and waist-to-height ratio, were measured using a multi-frequency bioelectrical impedance analysis for each subject. Semen analysis was conducted according to the World Health Organization laboratory manual for the examination and processing of human semen 5th edition. Linear regression models and unconditional logistic regression models were used to quantify the association between central obesity and semen parameters.

RESULTS

With adjustment for age, race, education level, marital status, fertility status, occupation, year of semen collection, abstinence period, ambient temperature, and relative humidity, central obesity defined as waist circumference ≥90 cm, waist-to-hip ratio ≥0.9, or waist-to-height ratio ≥0.5 was significantly associated with a 0.27 (95% confidence interval: 0.15, 0.38) mL, 14.47 (3.60, 25.34) × 106 , 7.06 (0.46, 13.76) × 106 , and 6.80 (0.42, 13.18) × 106 reduction in semen volume, total sperm number, total motile sperm number, and total progressive motile sperm number, respectively, and a 53% (10%, 112%) increase in odds of below the World Health Organization 2010 reference value for semen volume. These associations did not significantly vary across age. Similar results were observed for central obesity defined using each of the three indicators, except that subjects with a waist circumference ≥90 cm had a slightly higher total motility (estimated change: 1.30%; 95% confidence interval: 0.27%, 2.34%) and progressive motility (estimated change: 1.27%; 95% confidence interval: 0.23%, 2.31%).

DISCUSSION AND CONCLUSION

We found that central obesity was significantly associated with a reduction in semen volume, total sperm number, total motile sperm number, and total progressive motile sperm number. Future studies are warranted to confirm our results in other regions and populations.

Association between ambient temperature and semen quality among sperm donation volunteers in South China

BACKGROUND

Potential adverse effects of non-optimum temperatures on human semen quality have drawn much concern worldwide; however, the exposure-response relationship remains less understood.

OBJECTIVES

To quantitatively assess the association between exposure to ambient temperature and semen quality in South China, and to identify potential critical exposure windows.

METHODS

We conducted a longitudinal study to investigate 11,050 volunteers who lived in Guangdong province, China and intended to donate sperm in the Guangdong provincial human sperm bank during 2016-2021. Exposure to ambient temperature during 0-90 days before semen collection was assessed by extracting daily temperatures from a validated grid dataset at each subject's residential address. Linear mixed models and linear regression models were used to perform exposure-response analyses.

RESULTS

During the study period, the 11,050 subjects underwent 44,564 semen analyses. Each 5 °C increase of lag 0-90 day exposure to ambient temperature was approximately linearly associated with a 3.11 (95 % confidence interval [CI]: 2.08, 4.14) × 10⁶/ml, 9.31 (4.83, 13.80) × 10⁶, 1.27 % (0.91 %, 1.62 %), 8.20 (5.33, 11.08) × 10⁶, 1.37 % (1.01 %, 1.74 %), 8.29 (5.52, 11.06) × 10⁶, 0.67 % (0.28 %, 1.05 %), and 4.50 (2.20, 6.80) × 10⁶ reduction in sperm concentration, total sperm number, total motility, total motile sperm number, progressive motility, total progressive sperm number, normal forms, and total normal form sperm number, respectively (all p < 0.001), which was not significantly modified by age (all p for effect modification > 0.05). We identified a critical exposure period of 10-14 days before semen collection for sperm motility, and 70-90 days before semen collection for sperm count and morphology.

CONCLUSIONS

Our study provides consistent evidence that higher ambient temperature was significantly associated with a reduction in semen quality in South China. The findings highlight the needs to reduce high temperature exposures during 3 months before ejaculation to maintain better semen quality.