When IVF fails and the issue appears to be sperm-related, patients often ask why the clinic did not cancel the procedure if the sperm was “not good enough.” It is important to understand that semen analysis and sperm function tests are different.
A semen analysis only measures sperm count, motility, morphology, and pH. It is not a fertility test; rather, it assesses the testicles’ ability to produce sperm of reasonable quality. However, it cannot reliably determine a sperm cell’s fertilization potential.
Patients sometimes ask why they are not sent for a sperm function test instead. The reason is that not all centres have the technology to perform sperm function tests. In many cases, we only discover problems with sperm fertilization ability when we observe poor embryo development after IVF, despite having a good egg and an apparently normal semen analysis.
For a sperm cell to fertilize an egg—whether naturally, through IUI, or through IVF—it must successfully complete five key processes:
1. Capacitation – occurs inside the female reproductive tract; it cannot be evaluated directly.
2. Acrosome Reaction – the sperm’s ability to bind to the egg’s outer layer; this requires advanced technology to assess.
3. Zona Pellucida Binding – when enzymes in the sperm head are released, allowing it to penetrate the egg.
4. Nuclear Decondensation – the genetic material of the egg and sperm combine to form a fertilized ovum.
5. (Implied final step) Successful formation of a healthy embryo.
Because semen analysis cannot evaluate these functional steps, a sperm sample may appear normal yet still fail to fertilize an egg.
