Sydney

Fertility researchers have devised a way to isolate high-quality sperm from a sample of semen using an electric current. The team hopes that the method, which has resulted in the birth of a healthy baby, will lead to more efficient in vitro fertilization (IVF) treatments.

“We've been separating sperm in the same way since the first IVF baby Louise Brown was born, more than 25 years ago,” says Steven Fleming, scientific director of the Westmead Infertility Centre in Sydney. “No one has significantly moved the technology forward, until now.” Fleming hopes to collaborate with the researchers who developed the technique in clinical trials of the new method.

During IVF it is important to separate the sperm from the rest of the semen as quickly as possible because the semen contains potentially destructive oxidative chemicals. This is normally done by centrifugation, but the multiple steps necessary take up to an hour and the forces involved can damage the sperm. Centrifugation normally selects for higher-quality sperm, as sperm with dense intact heads are separated from the rest. Alternatively, sperm can be selected on the basis of their ability to swim.

Current methods to select sperm for IVF are slow and difficult. Credit: SCIENCE PICTURES LTD/SPL

But neither method works well when sperm samples have to be taken directly from the testicles. In this case, the resulting sperm aren't motile enough for a swim test and cellular debris makes centrifugation difficult.

The new method, developed by researchers at the University of Newcastle in New South Wales, relies on a technique known as electrophoresis, and the fact that negatively charged sperm have the most intact DNA (C. Ainsworth et al. Hum. Reprod. 20, 2261–2270; 2005).

Semen is placed in a chamber within a membrane containing pores through which only the sperm can pass. An electric current draws negatively charged sperm across the membrane, leaving the others, and any contaminants, behind.

It is not known why negatively charged sperm have the most intact DNA. Researchers think that negatively charged sialic acid, added during the final stages of sperm production, is an indicator that the sperm has successfully assembled and matured. “It's like the cherry on the cake,” says John Aitken, one of the researchers who developed the technique. “Everything else has to have gone absolutely normally for the sperm to get to that point.”

The new separation process takes only five minutes, is gentle, and works on sperm taken directly from the testicles. It also involves fewer steps than centrifugation, reducing the chance that samples could get mixed up.

Aitken and his colleagues collaborated with experts at an IVF clinic in New South Wales to treat a couple who had been unable to conceive using other methods of sperm separation. “Electrophoresis was tried as a last resort,” says Aitken. The couple conceived successfully and a healthy baby was delivered earlier this year. The researchers declined to reveal further details, saying they want to publish the results of the case study, but they plan to seek approval from hospital human ethics review committees to start a clinical trial next year.