精液质量分析与正常生育力的概念

Semen Quality Analysis and the Idea of Normal Fertility

世界卫生组织(WHO)为对精液质量参数提供参考范围,对《世界卫生组织人类精液分析实验室技术手册》(简称手册)进行了大幅修订。这引发如何定义"正常"(不包括用此概念表示高斯分布)的问题。其可作为一个纯粹的统计学概念,使用生物学上主观设定的切点值表示异常水平,通常为末端5%的人群。"正常"的另一定义也可根据生物学上常态和非常态的概念,表示生物学功能受损的临界点。这两者都可以用于描述性流行病学,例如研究变化趋势。但在考虑生育时,精液质量和生育力(使配偶妊娠的时间)两者都是连续变量,缺乏确定的阈值。手册使用了生物学意义上的"正常",因为提供的是在12个月或更短时间内使配偶妊娠男性的精液参数分布状态。但真正需要的却是反向的相同信息:获得一个特定的精液检测结果,预期生育能力如何,确定需要大概多长时间使配偶妊娠。从流行病学研究角度考虑,研究重点主要在于内部比较,而不是参考范围。如果更关注绝对值及其功能意义,换言之,如果精液分析数据从生物学角度上得到更好的校准,这将大有裨益。

The World Health Organization （WHO） has extensively revised its manual for semen analysis, and seeks to provide reference limits for semen quality parameters. This raises the question of what is meant by ＇normal＇ （excluding the use of this term to denote a Gaussian distribution）. It could be taken in a purely statistical sense, using a biologically arbitrary cut-off point to denote an abnormal level, typically the extreme 5 percent of the population. Alternatively, ＇normal＇ could be defined according to the biological concept of normality and abnormality, in terms of the point at which biological function becomes impaired. Either of these can be used in descriptive epidemiology, for example, to study trends, but in the case of fertility, both semen quality and functional fertility （time to pregnancy） are continuous variables with no clear threshold. The WHO manual uses the biological meaning of normal, in that it provides the semen parameter distributions for men who have recently fathered pregnancies that took 12 months or less to conceive. However, what is really needed is the same information the other way around： given a particular semen test result, what should be expected in terms of ability to conceive, and how long it is likely to take. In considering epidemiological research, the focus has been mainly on internal comparisons, rather than reference limits, but it would be beneficial if more attention were paid to the absolute levels and to what these mean in terms of function--in other words, if the data were better calibrated biologically.