The study, run by Dr Da Li at Shengjing University, challenges conventional wisdom that abstaining from sex between efforts to conceive can improve a couple’s chances of success.
The researchers looked at individual subjects’ semen after they had abstained for either several days or just an hour or two, comparing the volume of semen and the mobility of sperm in the samples.
They found that sperm swim fastest and are most likely to fertilise one to three hours after ejaculation. This was because sperm produced shortly after a man ejaculates have the greatest number of proteins that speed up movement.
According to Dr Li’s results, the longer semen exists outside the testicles, the more its sperm are vulnerable to DNA damage by oxygen, which could harm their ability to form an embryo.
“For years, men have usually been advised to limit sexual activity to increase the chances of pregnancy,” said Dr Li. “However, it’s time to change our minds. Our data indicates couples with relatively normal semen parameters should have frequent sex around the ovulation period.
“This could make all the difference to their efforts to start a family.”
To analyse the impact on fertility, Dr Li’s research team also ran a study of about 500 couples preparing for in vitro fertilisation (IVF) at a fertility clinic.
Researches asked men in the control group for semen samples after several days of abstinence, while men in the group under study abstained for less than three hours before providing their samples.
The IVF team proceeded as usual with the two types of sample, using them to generate and then implant embryos.
“A typical live birth rate in a cohort of this size is about 30 percent,” said Li. “In the experimental cohort, live births were higher by one-third.”
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