The New WHO

June 9th, 2010 § 12 comments

A first test of male fertility is the semen analysis.  You do your thing, and a technician counts the sperm, sees how they’re moving, what they look like and whether they’re alive.  For decades, the World Health Organization has published criteria for these numbers to alert a man that he might have a problem when it comes to impregnating a woman.  Until recently, the numbers were a consensus of expert opinion, but in the latest edition, the WHO criteria changed substantially.

What the WHO is currently doing is to dispense with expert opinion, and just lay the numbers out for all to see.  Table II from the paper shows the numbers for men from couples who conceived within a year.  Take sperm concentration, for example.  For centile 5, the sperm concentration is 15 million per ml.  That means that only 5% of couples where the man had 15 million/ml sperm or less conceived within a year.  For centile 50, the concentration was 73 million/ml, meaning that 50% of couples conceived within a year when the sperm concentration was up to that number.  You get the idea.

The problem is that people like cutoffs, and in the latest edition, the WHO chose centile 5 as the line in the sand.  It’s a good number for thinking that below it, couple infertility likely involves the male.  But keep in mind that at centile 10, only 10% of couples conceived within a year.  In other words, having sperm numbers above the centile 5 cutoff doesn’t guarantee that the sperm are trouble free.

Frankly, I think the WHO numbers are most useful to get a ballpark idea of how fertility may be related to what’s inside the semen.  I prefer the approach David Guzick and colleagues took, where they applied a statistical method called Classification and Regression Tree (CART) analysis to sperm, which gives two cutoffs in a “green light, yellow light, red light” fashion.  For example, CART analysis came up with 13.5 million/ml and 48 million/ml for sperm concentration.  At 13.5 million/ml sperm or less, the “red light,” couple infertility likely involves the male.  At 48 million/ml or more, your sperm probably are “green light” good to go.  Between 13.5 million/ml and 48 million/ml, the “yellow light,” sperm may or may not be the problem.  You can find the Guzick CART cutoffs here.

A lot of people, including doctors and fertility specialists, are confused about the new WHO cutoffs.  Expect a little consternation about them for a bit.

WHO Table II Distribution of values, lower reference limits and their 95% CI for semen parameters from fertile men whose partners had a time-to-pregnancy of 12 months or less

N Centiles


2.5 (95% CI) 5 (95% CI) 10 25 50 75 90 95 97.5

Semen volume (ml) 1941 1.2 (1.0–1.3) 1.5 (1.4–1.7) 2 2.7 3.7 4.8 6 6.8 7.6
Sperm concentration (106/ml) 1859 9 (8–11) 15 (12–16) 22 41 73 116 169 213 259
Total number (106/Ejaculate) 1859 23 (18–29) 39 (33–46) 69 142 255 422 647 802 928
Total motility (PR + NP, %)* 1781 34 (33–37) 40 (38–42) 45 53 61 69 75 78 81
Progressive motility (PR, %)* 1780 28 (25–29) 32 (31–34) 39 47 55 62 69 72 75
Normal forms (%) 1851 3 (2.0–3.0) 4 (3.0–4.0) 5.5 9 15 24.5 36 44 48
Vitality (%) 428 53 (48–56) 58 (55–63) 64 72 79 84 88 91 92

*PR, progressive motility (WHO, 1999 grades a + b); NP, non-progressive motility (WHO, 1999 grade c).

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§ 12 Responses to The New WHO"

  • Jennifer says:

    My husband and I have been TTC for 3.5 years. Our only issue appears to be male factor. My husband has had lots of semen analysis done over the years and we have tried every vitamin/herb combo, acupuncture, and clomid. At first we thought we saw improvement but then his numbers would crash again. After 3 years we see a distinct pattern. Late December/January his numbers fall into normal range, although still low. Then throughout the year they gradually fall, reaching as low as 100,000mil/ml by early Dec. Then just like that it resets and he’s back to his highest point. We’ve looked at stress levels, diet and activity and can’t figure out any reason for this pattern. We’ve seen it consistently for 3 years now. Any ideas?

  • Jennifer says:

    *edit…Oops, that’s 100,000/ml – not 100,000mil/ml.

  • maledoc says:

    Hi Jennifer, unfortunately I can’t answer personal medical questions on this site. It’s designed for general information about male fertility and potency. Medical problems are always best handled by a doctor in person. If you live near Chicago, I’d be happy to see your husband as a patient. Just call 312-440-5127 to schedule an appointment. A great place to find a doctor is the American Urological Association’s site.

  • me (statistician) says:

    Your interpretation of the figures is not correct I think. For example, for centile 5 the concentration is 15 million. This means that 5% of the men who got their partner pregnant in a year had a sperm count of 15 milion or less. NOT that 5% of the men with 15 million sperm concentration made their partner pregnant in a year.

    • Rebecca says:

      I was about to make this SAME comment. Your interpretation of the data is horribly flawed and I hope that people read the comments.

      It would be 5% of ALL men who impregnated their wives in a year, not 5% for men with that particular count were able to. We have no figures on how many men have that count and what percentage of them were able to conceive. That data is not present in the article.

  • maledoc says:

    Thanks, statistician: you’re absolutely right, and it’s a sleight of hand we clinicians often use in interpreting normative data to predictive ends. (It reminds me of Lippmann’s quote, “Everybody believes in the exponential law of errors: the experimenters, because they think it can be proved by mathematics; and the mathematicians, because they believe it has been established by observation.”) But you’re right, strictly speaking, it’s a normative statement, not a predictive one. Mea culpa 🙂

  • statistician says:

    Dear doctor,

    Thanks! In my opinion it does mean that the figures in this publication are more optimistic than what your interpretation suggests. Within a normally fertile group (i.e., pregnant within a year) there is 5% with sperm numbers below 15 milion. Hence the suggested cutoff by WHO (below 15 milion there is likely a problem), which fits quite well with what you describe David Guzick suggests.

    Best wishes!

  • well, i would say that infertility can be a thing of the past because of modern advancements in medicine `””

  • maledoc says:

    Someday infertility may be a thing of the past, but for the millions of couples who suffer with it, it is very much a problem of the present.

    • cp says:

      I agree. Infertility unfortunately will never be a thing of the past. I wish it would be. IVF doesn’t take away infertility. My husband has severe mfi and we have done 2 ivf and have one baby (plus 2 losses) as a result. We are still infertile since there is no reason and there fore no cure for my husband’s super low counts.

      Anyways I am glad to hear that the 15 mil/mL is only true for 95% of the men sampled.
      It makes me feel better that we may still have a chance of a natural conception, though the more time that passes that thought wanes. It doesn’t help that the only two pregnancies I had were a result of ivf + icsi. I wish they would make public the full results so we can know what the lowest count was that caused a natural pregnancy within a year.

  • Livasy says:

    Hi our family just loves your charming write-up thanx and pls stick to it

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