The Sperm Penetration Assay (SPA) checks to see if a man’s sperm can penetrate and fertilize eggs, and the SPA test is usually only performed when low IVF fertilization rates occur without any other explanation.
For sperm to fertilize an egg, they need to physically bind with the outer layer of the egg cell (the zona pellucida) and then release enzymes carried in the tip of its head to weaken and dissolve the tough outer coat of the egg’s shell. The DNA then needs to enter and fuse with the egg DNA to create a viable cell with its own unique collection of genetic material.
- The SPA specifically measures the sperm ‘capacitation’, which is the capacity of the sperm to make the complex membrane changes necessary to bind to, penetrate, and then fertilize an egg
- Capacitation of sperm usually becomes activated when they come into contact with a woman’s fertile mucus
- Sperm unable to perform these actions can’t fertilize eggs, which occurs in about 5% of men tested
How is the SPA done?
- Specially prepared hamster eggs are used in this test
- By measuring how well a man’s sperm can penetrate the hamster eggs, it’s possible to calculate his sperm’s ability to penetrate human eggs
What does it tell you?
The results from a SPA test help to identify men whose sperm can’t fertilize eggs. These men will usually be told their best chance of having a baby is with intra-cytoplasmic sperm injection (ICSI) as it avoids the issues of sperm binding to and penetrating eggs.
Recent trends in assisted reproductive techniques (ART) have seen a big increase in ICSI (despite the costs being higher), with 66% of all IVF procedures in the USA using ICSI in 2011. i This decision by clinics to use ICSI so often indicates that they believe egg penetration/male factor infertility is a significant issue for many couples having IVF treatment.