An 'entrance exam' set by the cells that line the womb can determine whether or not human embryos are able to implant into the womb's lining, according to researchers.

Not all embryos are viable and those that contain genetic mutations may not be able to implant, or may implant but miscarry at a later stage. Approximately 15 percent of clinically recognised pregnancies result in miscarriage and around half of early stage miscarriages are due to chromosomal abnormalities.

The study, led by Warwick Medical School and University Hospitals Coventry and Warwickshire NHS Trust, shows that high quality embryos secrete a chemical called trypsin, which signals to the womb to prepare its lining and create a supportive environment in which the embryo can be implanted. Conversely, embryos that are developmentally impaired cause a stress response in the womb, which leads to rejection of the embryo.

The research was conducted using the medium that the embryos grew in, comparing a group of 40 embryos that resulted in pregnancy with a group of 49 embryos deemed as poor quality and unsuitable for transfer. The medium from these embryos was incubated with human endometrial (womb) cells and the effects on the cells were analysed.

Study co-author Professor Jan Brosens likens the implantation process to an entrance exam, explaining that 'a poorly prepared womb will either make the test too rigorous or too lax – decreasing the chances of a successful pregnancy'. If the test is too difficult, even embryos that are developmentally normal will be eliminated, and if it is too lax, abnormal embryos will be able to implant.

The researchers believe that their findings could in future be useful to those undergoing IVF, since implantation failure is one of the main reasons why IVF is unsuccessful. Knowledge of the factors which alter the implantation process may help lead to treatments that optimise implantation rates.

'What we're looking at now is how to alter the lining of the womb so it can set this entrance exam at the right level and prevent implantation failure and miscarriages', said Professor Brosens.

Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.