Fast-Freeze May Help Sperm Survive Storage, Study Finds

Method might pave way for HIV-positive men to donate sperm safely, researchers say

TUESDAY, Sept. 14 (HealthDay News) -- Researchers say they have developed a new and better method of freezing human sperm for later use in pregnancy attempts.

The new technique could potentially improve in vitro fertilization treatment and perhaps make it possible for HIV-positive men to donate sperm safely, the researchers say.

The freezing approach used in the study is already used for embryos and eggs, "and this is the next step, so it is logical," said Dr. Ian Cooke, emeritus professor of obstetrics and gynecology at the University of Sheffield in England, who is familiar with the study.

"Any improvements in sperm freezing would be welcome," said Mathew Tomlinson, a fertility specialist and scientist at Nottingham University Hospitals in England.

"We can store sperm for many years, but only 25 to 30 percent of sperm survive from even the best samples," said Tomlinson.

Among cancer patients who want their sperm stored before they undergo chemotherapy, as little as 5 percent of sperm may survive, he added.

When study lead author Raul Sanchez of La Frontera University in Chile and colleagues tested their alternative freezing approach, known as vitrification, they found that almost 80 percent of sperm remained viable after thawing.

In the traditional approach, sperm is frozen slowly and stored in liquid nitrogen. Vitrification involves removing the plasma in sperm, suspending the sperm in a sucrose solution and fast-freezing it in liquid nitrogen. It is then stored in liquid nitrogen or another kind of deep freeze.

This process results in greater sperm vitality and motility, and is less damaging to sperm, the researchers explained in a news release from the International Federation of Fertility Societies.

Because the sperm plasma -- potentially home to the virus that causes AIDS -- is extracted, the researchers think their approach may also allow HIV-positive men to donate sperm without passing on the illness to a mother or baby.

But Dr. Robert D. Oates, professor of urology at Boston University School of Medicine, said he's skeptical of the researchers' claims. The findings don't "translate directly into anything related to whether this allows better pregnancy rates," he said.

Moreover, the research doesn't prove that the freezing approach leaves the sperm free of disease, he added. "This is a technique that may have an application," Oates said, "but their claims are way overstated."

The findings are scheduled for presentation Tuesday at the World Congress on Fertility and Sterility in Munich, Germany.

More information

The U.S. National Library of Medicine has details on semen analysis, which measures the quality of sperm.

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