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Sperm Washing: How It Works

The sperm washing procedure involves spinning a semen sample in a centrifuge to separate it into three parts. Those parts can then be tested for HIV. Some researchers believe that the virus is carried in seminal fluids outside the sperm cells. The technique, therefore, might be used to isolate HIV from sperm cells, which can then be used to impregnate a woman via artificial insemination. But, doctors warn, no method is foolproof.

Semen is put in a centrifuge tube, along with a more dense solution. The solution helps to separate the semen as it is spun in the centrifuge.

After being spun in the centrifuge, the specimen divides into three parts
Once they are separated, each of these parts are subjected to testing.

Seminal Fluids:
Tested for HIV

Other Cells:
Tested for HIV

Sperm Cells:
Half of the sperm cells are frozen for possible in vitro fertilization.

The other half of the sperm cells are tested for HIV.

Conceiving Without Transmitting

There's more than one way for HIV positive couples to attempt a safe pregnancy. In theory, procedures like sperm washing are fairly straightforward -- collect the semen of an HIV-positive man and rinse away the parts of it that carry the virus. In practice, though, the undertaking raises complicated questions.

Sperm washing is actually a common technique. It's been used for years by infertility clinics to boost the potency of a man's semen when trying to help his female partner conceive. It takes advantage of the fact that sperm are small and heavy, and can move like tadpoles. The semen is put in a test tube which is then spun in a centrifuge to separate the sperm from the other cells and fluids. The non-sperm part of the semen is removed, and each fraction is tested for HIV. If both parts are negative, the isolate sperm are covered with a new solution, which the healthiest cells will swim their way into. If no virus is found in a second test on the sperm, they can be used to fertilize the woman's egg cells.

There are currently three ways to attempt pregnancy using washed sperm. A common method used for years is intravaginal insemination, which involves holding a cervical cap full of live sperm near a woman's cervix and allowing them to swim into the uterus. Dr. Ann Kiessling, director of the Assisted Reproduction Foundation in Boston, says this procedure may be safe, but hasn't been tried. But, she adds, the safest method is in vitro fertilization, which only exposes the woman to fertilized eggs, and not to live sperm cells.

A third method, called "intrauterine insemination," or IUI, has been used by HIV couples in Italy, the UK, Spain and Switzerland. It involves inserting a catheter filled with washed sperm directly into the woman's uterus. Dr. Augusto Semprini, an Italian researcher who first applied IUI to HIV cases, claims to have achieved more than 250 pregnancies without a single viral transmission to either mother or child. But Dr. Kiessling remains cautious. IUI, she says, can leave the woman exposed to any trace cells that aren't filtered out in the washing process or detected by microscopic evaluation. And, she adds, it requires about ten times as many sperm cells as IVF, and can be an uncomfortable, invasive procedure.

All three of these methods rely on the belief, shared by many researchers, that HIV lurks in white blood cells and the fluid parts of semen. That would make sperm-washing a potentially safe way to impregnate an HIV-negative woman with the sperm of her HIV-positive partner. Some scientists believe that sperm-washing can reduce the level of HIV in an infected man's semen by 100,000-fold.

But that's not enough to convince the Centers for Disease Control and Prevention in the United States, and the legality of IUI stands on shaky ground in the U.S., where it's illegal in some states to transfer HIV-infected blood or tissue from one person to another. Those laws could be interpreted to include methods like this one, that assist in reproduction.

Beyond the legal questions are the scientific ones. Sperm washing appears to effectively separate sperm cells from infectious agents in semen, but exactly how thorough it is hasn't been quantified. Some researchers also wonder whether HIV can be carried in the actual sperm cells of men who have been infected for a long time. If that were the case, then separating those cells from white blood cells and other fluids would still leave the mother and her child open to infection.

Sperm-washing combined with IUI did result in one man passing the virus to his partner in this country. The woman sued her doctor, though it remains unclear whether her infection was caused by the procedure. Health care professionals willing to undertake the sperm-washing venture are quick to remind their patients that it is only a risk-reduction method, and that no procedure is entirely risk-free.

But those cautionary words can be forgotten amidst the flurry of anticipation for couples who, not so long ago, thought they would never be able to consider raising a family. As drug therapies allow people infected with HIV to live longer, the demand for reproductive strategies is expected to rise. In Europe , doctors are fielding an increasing number of inquiries about how to conceive children without passing on the virus. They may find that convincing anxious parents of the lack of certainty in the process is as challenging as carrying it out.

Article and Artwork: Robin Marks

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