I was at a meeting this past weekend, and one of the hottest topics of discussion was sperm shape. We call it “morphology”, and it’s how sperm look under the microscope. A technician counts up the number of normal looking sperm, and reports the percentage of the total. Here’s the odd part: with fairly generous criteria, (like normal means one oval head with one tail,) only about a third of a man’s sperm look normal. That means, for most men, most of their sperm are funny looking.

Is that a bad thing? Well, we all managed to get here with fathers that had for the most part funny looking sperm. Was it the best looking sperm that found its way into the egg and made you? That’s the million dollar question, and one for which we don’t yet entirely know the answer.

There are two ways to measure the look of sperm. One is using the World Health Organization (WHO) criteria, which for the most part say that if a third of sperm look fairly normal, the whole lot are O.K. These criteria have been around for a while, about a half century. The new kid on the block is about twenty years old, and uses a much stricter definition to call a sperm ‘normal’. Thinus Kruger invented this stricter system, and so it’s often called ‘Kruger morphology’ or ‘strict morphology’. To calculate strict morphology, the technician takes measurements of the sperm, and if any are outside the normal range, the sperm is counted as abnormal. The usual cutoff for strict morphology is 4%, which means that 95% of your sperm can be funny looking, and you’d still be considered to have normal morphology. That should give you an idea of how oddly shaped most sperm are in the typical male.

One big challenge in assessing morphology is that even though it appears to be an objective way to describe sperm shape, it still includes a great deal of subjectivity on the part of the technician. The technician is like a referee. Sometimes he or she will let a sperm pass the shape test, sometimes not. From some labs, almost no sperm are called normal in shape. So the first thing you’ll want to do if you’re told that your sperm are especially strangely shaped is to have the test repeated, preferably at a lab that does a lot of semen analyses.

For as many scientific studies that say morphology predicts how sperm do, there are those that say it doesn’t. You might think, as I did, that if a man has especially odd looking sperm, it would affect the chances of sperm getting into the egg and be a good reason to have the sperm injected into the egg using intracytoplasmic sperm injection (ICSI). ICSI is a technique used in in-vitro fertilization (IVF) where the sperm is injected directly into the egg. But in 2007, Keegan and colleagues published a study which reported that there was no advantage to using ICSI for semen with an abundance of funny looking sperm, meaning they did just as well getting inside the egg by themselves as men with “normal” looking sperm.

What does this all mean? Well, it could mean that sperm shape counts, but we don’t yet know how to measure it correctly. Or it could mean that the sperm shape doesn’t have much to do with its function–in other words, the shape of the boat doesn’t say much about how good the captain is that’s piloting it. I don’t know which is right, and I don’t think anyone does yet. So if someone tells you that your sperm is funny looking, don’t despair. It might not be the thing keeping your wife from getting pregnant.