MADRID, Spain (AP) -- New research suggests there is little value in couples abstaining from sex to improve their chances of conceiving by saving sperm for the woman's most fertile time of the month.

In a study to be presented Monday at a European fertility conference, Israeli scientists provide the strongest evidence yet that men with low sperm counts can significantly reduce sperm quality by holding back for longer than a day or two.

They found that the performance for men with normal fertility tests remained the same whether they abstained from sex for one, two or 10 days before providing a sample.

"Long residence in the male reproductive tract might in some cases mean the sperm do worse, perform worse, than they could do if they abstained less," said the study's leader, Dr. Eliahu Levitas of Ben-Gurion University in Israel.

The finding appears to challenge the role of abstinence in male infertility treatment. World Health Organization laboratory guidelines recommend that men seeking fertility treatment refrain from sex for between two and 7 days before providing a sample for analysis.

In the new study, to be presented at the annual conference of the European Society of Human Reproduction and Embryology, Levitas' group analyzed more than 7,200 semen samples from about 6,000 men undergoing routine fertility investigations.

More than 4,500 of the samples were normal, while the rest showed varying degrees of low sperm counts.

The men abstained from sex for up to two weeks before giving their samples.

In men with low sperm counts, the researchers found the volume of semen increased after prolonged abstinence, but the quality got gradually worse the longer the men held back.

The number and proportion of motile sperm, meaning active and moving sperm, fell significantly from day two onwards, reaching a low at day six and remaining low.

The percentage of malformed sperm also increased after just a few days of abstinence, the scientists found.

"If a man abstains for two days instead of five days, that may make the difference," particularly in fertility treatment that involves artificial insemination, Levitas said, because that procedure demands the best quality sperm.

In normal men, the study found no change in sperm motility. The percentage of malformed sperm increased only after 11 days, and then only so marginally that it is unclear whether it could affect fertility.

"There is no point in giving up sex to save up sperm," said Dr. Karl Nygren, a fertility specialist at Sophia Hospital in Stockholm, Sweden, who was not connected with the research.

The argument in favor of abstinence is that it may increase the volume of semen and hence number of sperm in an ejaculate.

"You may have more sperm and more semen volume, but the quality is less. Usually, fresh sperm are better than stale sperm," said Lynn Fraser, a professor of reproductive biology at King's College in London. "What you really want to do is flush the system out so that the sperm that are there are fresh."

The optimal strategy for couples with no fertility problems who are trying to have a baby is to have sex once every day or two around the time of ovulation, she said.

"Realistically if people want to have children, you wouldn't want to have intercourse three times a day every day because that might deplete the pool that you have," said Fraser, who was not involved with the study. "But there's a lot to be said for keeping the system in a state whereby most of the sperm that have accumulated haven't been there very long."

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