Sperm assessment

Raman spectroscopy could enable fertility researchers and IVF clinicians to assess individual sperm. The process involves capturing an individual sperm cell between two highly focused beams of laser light with Raman pinning down features of the trapped wriggler's DNA.

Researchers at the University of Edinburgh, with funding from the UK's EPSRC (Engineering and Physical Sciences Research Council), have demonstrated that they can obtain a chemical "fingerprint" for individual sperm sperms that is directly correlated to the quality of the sperm and so represents a way to assess the chances of whether the sperm will be capable of fertilising an egg in an in vitro fertilisation (IVF) procedure.

Team leader Alistair Elfick explains how he and his colleagues can trap individual sperm cells between two highly focused beams of laser light - so-called optical tweezers. They then use Raman spectroscopy to characterise and assess the sperm's genetic material. Powerful statistical analysis of the Raman results allows the team to build up knowledge of how damage DNA vibrates compared to good DNA. This is the first time scientists have used such a process to evaluate DNA damage in sperm.

"In natural conception the fittest and healthiest sperm are positively selected by the arduous journey they make to the egg," explains Elfick, "What our technology does is to replace natural selection with a DNA-based ?quality score?." He asserts that this technique is not about the ethic minefield that is known colloquially in the tabloid media as creating "designer babies". "We can only tell if the sperm is strong and healthy not if it will produce a baby with blue eyes," Elfick confirms.

Previous quality control tests on sperm have generally considered the shape and motility, or activity, of sperm. While these do give an indication of the general health of a sperm they do not reveal the quality of its genetic payload, which is more important to successful conception and the development of a health embryo than how wriggly is the sperm's tail.

Some form of infertility affects at least one in six couples in the UK. In around fifty percent of cases, it is problems with sperm production that is to blame for failure to conceive. IVF, and intracytoplasmic sperm injection (ICSI), in which sperm are injected into the egg has solved this problem for many childless couples.

There are, of course, established tests for sperm DNA quality. However, these work by cutting the cells in half and tagging the DNA with a fluorescent dye, which inevitably kills the sperm and renders it useless for IVF. The new process developed by Elfick and colleagues, while handling the sperm with laser beams does not destroy the sperm. If the assessment reveals the sperm to have good DNA quality then it can still be used in a round of IVF.

Research has shown that conception success rates in sexual intercourse and IVF treatment are approximately one in four. The researchers hope that by giving IVF clinicians the ability to select the best quality sperm they should be able to improve the chances of conception, perhaps outstripping natural conception methods. The new work suggests that this approach to IVF could give the child the best start in life.

The research is only in the early pre-clinical phase of testing, however, and the researchers say that complete trials will take some time yet. The approach may not be available to patients for at least five to ten years. Part of the ongoing research will involve assessing whether the optical tweezers or the Raman laser affect sperm cells at the genetic level. Laser damage in this kind of operation with other cells has not previously been observed, but, says Elfick, "we need to be absolutely sure that this is the case for sperm too."