New research by Israeli fertility experts has challenged current medical opinion, which holds that refraining from sex for up to a week is beneficial for men prior to undergoing some types of fertility treatment.

Doctors from Soroka University and Ben-Gurion University tested over 7,200 semen samples for semen volume, sperm concentration and shape, and the percentage and total count of motile (active and moving) sperm. The samples were from around 6,000 men being investigated or treated for infertility who had abstained from sex for periods of up to two weeks.

More than 4,500 of the samples had normal sperm counts while the remainder had varying degrees of oligozoospermic (reduced) counts ranging from mild, through moderate, to severe.

The researchers found that while the volume of semen increased up to 11 to 14 days of abstinence, whatever the sperm count was, the morphology (shape and form) of the sperm gradually deteriorated.

In the samples from men with reduced sperm counts the proportion of motile sperm actually fell significantly from day two onwards, reaching a low at day six and remaining low.

Dr. Eliahu Levitas will tell the annual meeting of the European Society of Human Reproduction and Embryology in Madrid: "Semen volume was directly and significantly correlated with duration of abstinence, while sperm motility was inversely and significantly related to abstinence in oligozoospermic samples only. The percentage of normal forms of sperm was inversely and significantly related to abstinence in both moderately oligozoospermic and normal samples."

Dr. Levitas, a senior physician at the fertility and IVF unit of Soroka University Medical Center, said that most fertility clinics followed the World Health Organisation guidelines of recommending sexual abstinence for two to seven days prior to treatment.

"Our data challenge the role of abstinence in male infertility treatments. What we have found is not so relevant to ICSI, where only a single sperm is injected into the egg, but for those treatments where we are trying to get the best possible sperm quality for intra-uterine insemination.

"For these patients we recommend minimal abstinence - ideally no more than two days."

Dr. Levitas said there was no real consensus among researchers as to why sperm gets damaged and becomes less viable. "It's possible that there is oxidative DNA damage by, for example, cigarette smoking or other damaging agents. Or perhaps the sperm from oligozoospermic men is more susceptible to detrimental agents and therefore might benefit from spending only a short time in the reproductive tract."