Regional Differences in Semen Quality Between Guangzhou and Hong Kong in South China: A Cross-Sectional Study

Abstract Background: The geographic variation in semen quality has been reported in many countries. However, the situation in China is still unknown. To answer this question, we examined the variation in semen parameters between two cities in south China: Guangzhou (GZ) and Hong Kong (HK).Methods: Semen analysis data of 13507 subjects from GZ and 1106 subjects from HK were retrospectively analysed. In order to control for referral bias, we selected two well-defined subpopulations, namely, subpopulation Ⅰ: male partners of women with an underlying cause of subfertility, which is assumed to be similar to the general male population; subpopulation Ⅱ: normozoospermic men, which is assumed to represent men with normal spermatogenesis, sperm maturation and sperm transportation. In addition, we have also chosen to control for two well-recognized confounding variables, namely, age and abstinence time by using a case matching design and generalised additive models (GAM).Results: In using the case matching design, subjects from different cities with similar age and abstinence time were matched. The results of the paired T test showed that sperm concentration and motility of subjects in HK were significantly lower than that of subjects in GZ in both subpopulation Ⅰ and Ⅱ (P < 0.05); on the other hand, the sperm morphology of subjects in HK was significantly lower than that of subjects in GZ in subpopulation Ⅰ (P 0.05).The results of GAM model showed that the sperm parameters were variated by age and/or abstinence time, however, the sperm concentration, motility and morphology of subjects in HK were significantly lower than that of subjects in GZ in both subpopulation Ⅰ and Ⅱ (P < 0.05). Conclusions: The semen quality of subjects in HK was significantly worse than that of subjects in GZ, which may be caused by environmental and lifestyle factors, given that the study subjects in both cities of the present study are of the same ethnic origin.Trial registration: Not applicable.