Couples who are trying to have a child together may benefit from having sex twice in one night – and not for the obvious reason.
Scientists discovered sperm collected three hours after a man has already ejaculated swims fastest and is most likely to fertilise an egg.
And using sperm produced no more than 180 minutes after a man last climaxed can also boost IVF success rates by a third, they found.
The Chinese findings contradict the myth it takes a man between 24 and 36 hours to ‘replenish’ his sperm bank after ejaculating.
Infertility strikes around 11 per cent of women and nine per cent of men of a reproductive age in the US. And figures suggest around one in seven couples have difficulty conceiving in the UK.
Semen samples were taken from 250 men both a couple of days and several hours after they last ejaculated.
Researchers led by Dr Da Li at Shengjing Hospital then compared the volume of sperm and their speed between the different samples.
They found sperm produced shortly after a man ejaculates has the greatest number of proteins that speed up their movement.
And the fresh sperm also have higher levels of proteins that are required for them to fuse with an egg.
In a second part of the experiment, around 500 couples who were preparing for IVF were also assessed.