Doctors try to better understand embryo implantation in IVF

Medical researchers are using animal models in an attempt to understand human embryo implantation failure, something of a mystery in female fertility.

In an effort to improve the success rate of IVF and assisted reproductive technologies, researchers at Baylor College of Medicine in Texas, have been investigating exactly what is involved in successful embryo implantation. The team discovered that a protein called 'follistatin' plays a key role in establishing how receptive the uterus is to embryo implantation, in an animal model. The results, published in the Proceedings of the National Academy of Sciences, contribute to the understanding of embryo implantation and may provide new insights into human embryo implantation failure. The complex process of embryo implantation in the uterus has raised interest among researchers in the field in part because it fails in about half of IVF procedures. Dr Diana Monsivais, a postdoctoral fellow in pathology and immunology at Baylor College of Medicine, says that a better understanding of the process would help raise the odds of successful attempts at in vitro fertilisation:

"Embryo implantation into the uterus wall is a highly coordinated process that involves many proteins and communication between the embryo and the mother. If this communication fails, the embryo won't attach to the uterus and a new life won't develop."

In this study, the researchers genetically engineered mice to lack follistatin in the uterus and determined the effect on mouse female fertility:

"Follistatin was already known to be important after implantation. It promotes the decidualisation of the uterus, that is, the changes in the uterus that are necessary to support and nurture the embryo as it develops."

Female mice that lacked follistatin in the uterus produced fewer pups per female and fewer litters than normal mice. Careful assessment of implantation in these mice revealed that the embryos do not attach to the uterine wall. They float inside the uterus. Because they fail to attach to the uterine wall, the embryos do not trigger decidualisation. Dr Martin Matzuk, professor of pathology and immunology, says embryo implantation is like a black box:

"The discovery that follistatin is an important protein that is required for successful mouse embryo implantation can help us develop strategies that might improve the success rate of human embryo implantation procedures in the assisted reproductive technologies clinic. I think that embryo implantation is like a black box, and a mouse model is a great tool we can use to get insights on how that black box might work in humans. This study opens the possibility of identifying biomarkers, that is, compounds, such as follistatin, that could work as clues that tell us the best time to transfer an embryo to a woman attempting IVF and improve the chances of a successful implantation."