WHO semen reference values using evidence-based data mark changes

Q. The fifth edition of the World Health Organization reference values for human semen characteristics is a substantial departure from previous editions. Can you explain conceptually the difference between this edition and previous ones?

A. I think there are three main differences. First is the introduction of new reference ranges, which-as far as I'm concerned- are evidence based for the first time. They may not be perfect, but they are based upon real-live data. In the past, it was my understanding that the reference values were determined by committee, based upon some pretty good guesswork but not on any recent studies.

Third, we now have much more in the way of evidenced-based technique in the laboratory. I like the fact that laboratory scientists have much more evidence to support what they do. The obvious example is weighing of semen containers to estimate the volume of semen ejaculated. We introduced that recently into my lab, and there's been a profound difference in the results we generate. We're seeing semen volumes that have increased by about 0.5 mL just by changing technique.

Q. You speak of this edition as being, for the first time, evidence based. What populations were studied for these reference values?

A. The paper that those reference values are based on, which is as close as we're going to get to a meta-analysis of this data in our history, consisted of almost 2,000 men whose partners had conceived within 12 months of ceasing contraception. In other words, the population consisted of recent fathers and time to pregnancy of less than 12 months. They provided a single semen sample, and the semen analysis was performed entirely in the laboratory where there is an element of certainty that good technique was being used. There are some caveats here that are interesting to consider, but are probably beyond the scope of this discussion.