Ejaculate Volume Is Seriously Underestimated When Semen Is Pipetted or Decanted Into Cylinders From the Collection Vessel

Abstract

The total sperm count (number of spermatozoa per ejaculate) rather than sperm concentration (number of spermatozoa per unit volume of semen) is the more important semen variable related to fertility. It reflects testicular volume (Handelsman et al, 1984; Andersen et al, 2000; Behre et al, 2000), and thus is a measure of total testicular sperm output (MacLeod and Wang, 1979), which is directly related to the chances of pregnancy after coitus. The concentration of spermatozoa in the ejaculate, however, depends on the extent of dilution of epididymal spermatozoa by secretions of the prostate and seminal vesicles occurring at ejaculation and is therefore influenced by the secretory capacity of the accessory sex glands. This is an important distinction, for when comparing semen quality from older and younger men, sperm concentrations do not differ, yet semen volume is reduced in the older men, and so the total number of spermatozoa per ejaculate is lower in the older men (Ng et al, 2004; Nieschlag et al, 1982). The total number of spermatozoa per ejaculate is obtained by multiplying the concentration of spermatozoa by the semen volume. The latter is best measured by weighing (Eliasson, 2003), assuming a density of 1.0 g/mL (Auger et al, 1995; Jorgensen et al, 1997, 2001; Brazil et al, 2004), but alternative methods, such as collection into graduated cylinders (Behre et al, 2000), pipetting from the collection vessel (Mortimer 1994; Jorgensen et al, 1997), and pouring from the collection vessel into a graduated tube (Jorgensen et al, 1997), are in current practice. Two recent studies have found that pipetting semen from the collection vessel leads to an underestimation of about 0.5 mL (range 0.3–0.8 mL; Brazil et al, 2004; Iwamoto et al, 2006) compared with weighing, but no data are available about losses incurred when pouring semen into graduated cylinders. Because the area of contact with the sides of the collection vessel while decanting semen into a graduated cylinder is likely to be far larger than that during pipetting, retention within the vessel could be much larger, leading to a larger underestimation of volume with this method. In this study, new data are obtained on the loss of semen volume during decanting to a cylinder and previously published results on losses because of pipetting, and the density of semen is reanalyzed together with additional data.