HOW LONG DOES IT TAKE?

This week: For sperm to meet an egg

THE short answer is up to five days, but the actual time varies depending on how far from ovulation intercourse takes place, says Allan Pacey, a professor of andrology at the University of Sheffield.

‘Sperm can survive in the fallopian tubes for five days if ovulation has not yet happened.

‘If it has, however, then a sperm can probably reach the waiting egg within 30 to 60 minutes of intercourse.’

During ejaculation, around 250 million sperm are released — but only one will get through the reproductive tract and fertilise the egg. Around 99 per cent will die before they even reach the cervix. Others can’t get in the fallopian tube or choose the wrong one — women have two, and only one will contain an egg. This means that only around 100 sperm are in the final race to enter the egg — and as soon as one does the egg’s shell hardens so that no other sperm can enter.