Teratozoospermia: what abnormal sperm morphology means
Teratozoospermia means fewer than 4% of your sperm have a textbook-normal shape. It is the semen parameter that causes the most alarm and predicts the least — men with 1% or even 0% normal forms conceive naturally more often than the number suggests.
Why the percentage looks so low
Almost all labs grade morphology using Kruger strict criteria, which judge each sperm against an idealised template and reject it for even minor deviations in head shape, midpiece, or tail. Under this method, a completely fertile man typically scores somewhere between 4% and 15% normal forms. Scoring 96% "abnormal" is the normal human condition, not a disease.
This is why the WHO threshold sits at 4% — it is the 5th percentile of men whose partners conceived within a year, not a measure of how many sperm are damaged. A result of 3% is meaningfully different from 15% in a statistical sense, but it is not the catastrophe the framing implies.
Morphology also has the poorest reproducibility of any semen parameter. Different technicians grading the same slide often disagree, and the same man can score 2% and 6% on samples taken weeks apart. Treat a single morphology number as a rough signal, not a verdict.
What it means for fertility
Isolated teratozoospermia — low morphology with normal count and motility — has only a weak association with time to conception. Multiple large studies have found that morphology alone is a poor predictor of natural pregnancy, and many clinics now weight it far less heavily than they did a decade ago.
Morphology matters more when it is low alongside count and motility, which together indicate a broader production problem (see OAT syndrome). It also matters more for IUI success than for IVF, and barely at all for ICSI, where an embryologist selects individual sperm by eye.
One exception deserves attention: globozoospermia, a rare genetic condition in which every sperm has a round head and lacks the acrosome needed to penetrate an egg. This is a true 0% morphology with a specific structural cause, and it does require ICSI, sometimes with assisted egg activation.
What to do about it
The most useful response to an isolated low morphology result is to look at the whole picture rather than fixate on the number. If count and motility are healthy and you have been trying for under a year, continuing to try is a reasonable plan.
The lifestyle factors that influence morphology are the same as for other parameters — heat, smoking, alcohol, obesity, and oxidative stress — and a varicocele can affect shape as well as count. Improvements are usually modest, and again take three months to appear.
If you have been trying for over a year, or if morphology is low alongside other abnormal parameters, that is the point to see a reproductive urologist rather than to keep optimising supplements.
FAQ
Is 2% sperm morphology bad?
It is below the WHO threshold of 4%, but far less concerning than it sounds. Men with 1–2% normal forms conceive naturally, and morphology on its own is a weak predictor of pregnancy. If your count and motility are normal, a 2% morphology result is not usually a reason to change your plans.
Can you get pregnant with abnormal sperm morphology?
Yes. Isolated low morphology has only a modest effect on natural conception rates. Where it does matter, IUI and especially IVF with ICSI are very effective, since ICSI lets an embryologist select a normal-looking sperm and inject it directly into the egg.
Why is my morphology 0%?
A 0% result most often reflects strict grading, technician variation, or a borderline sample rather than a true absence of normal sperm. Repeat the test before drawing conclusions. Genuine, persistent 0% morphology can indicate globozoospermia, a rare genetic condition affecting sperm head structure, which is diagnosed by a specialist.
Can sperm morphology be improved?
Modestly. Stopping smoking, reducing alcohol, avoiding scrotal heat, losing excess weight, and treating a varicocele can all shift the number, but morphology tends to respond less dramatically than count or motility. Allow three months between any change and a retest.