Healthy sperm are vital for achieving pregnancy. But what are the key factors for them to be in tip-top condition?

Firstly - quantity. For the best chance of fertilisation, you should have more than 20 million sperm per ml of semen. Only 200 of these will actually reach the fallopian tube, and one will make it through to fertilise an egg.

Next - quality. The shape and structure (or morphology) of your sperm are important too. A normal sperm has an oval head and a long tail for swimming, and you need more than one-third normal sperm for good fertility.

And finally - motility. Sperm have to move on their own to reach and penetrate the egg. So, motility is key, and you need at least half to be moving to characterise healthy sperm.

To make sure your sperm are as healthy as they can be, make sure your testicles stay below 32^oC. Have a shower instead of a hot bath, stay out of the sauna or jacuzzi, and try not to sit or drive for too long.

The old tale is true: wear loose fitting cotton boxer shorts instead of tight briefs, and avoid synthetic fabrics. Some like it hot - but not sperm…