Abstaining from sex in order to store up sperm and maximise the chance of a pregnancy is not just a waste of time for men with normal sperm counts, but positively detrimental for those with low counts.
The new research overturns a long held view that men with reduced sperm counts should not ejaculate for at least a week before giving a sample for use in some types of fertility treatment.
Scientists in Israel tested over 7200 semen samples for qualities including sperm volume, shape and speed. For all the men, the volume of sperm produced increased as the period of abstinence lengthened up to 11 to 14 days.
However, for those with low counts, the shape and motility of the sperm began to deteriorate after just two days of abstinence. For those with normal sperm counts, abstinence made no difference to the sperm's quality.
"Our data challenge the role of abstinence in male infertility treatments," says Eliahu Levitas, from Israel's Soroka University, who presented the work at the European Society for Human Reproduction and Embryology in Madrid on Monday.
The findings may be most pertinent for couples attempting to conceive via intra-uterine insemination, in which semen is injected through the cervix directly into the woman's uterus.
It is often the first option tried by couples unable to conceive naturally. "For these patients we recommend minimal abstinence - ideally no more than two days," Levitas says.
The findings should not alter the approach to treatment called intracytoplasmic sperm injection (ICSI), where a single sperm is injected directly into an egg.
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