Facts about fertilisation

1. A woman’s entire supply of eggs (several million) is created while she herself is still in the womb. By puberty these have dwindled to between a quarter and half a million. During her life only 400 or so of these will be released via ovulation.

2. It takes 380 cell divisions to make one sperm, compared with only 23 cell divisions for one egg.

3. Up to 1,500 sperm per second are produced in each testicle

4. Most healthy sperm can live in the female reproductive tract for several days, which means that intercourse can take place up to three days before ovulation and fertilisation will still be possible

5. An adult male ejaculates many millions of sperm each time and the egg is 500 times wider than the head of the sperm.

6. But despite the size of its target and sheer weight of numbers, just a hardy 200 or so will go the distance required – through the cervix and uterus to the Fallopian tubes - to fertilise the egg and make a baby.