Scientists have discovered why some embryos fail to implant in the womb which could lead to new treatments for thousands of infertile couples. For the first time, scientists have discovered the process that allows the embryo to latch on to the womb lining and create a successful pregnancy. The team at Oxford University have filmed the event in detail in the laboratory.
Fertility experts said the reason why some perfectly healthy embryos fail to implant in the womb has remained a mystery of human reproduction and the findings are "very exciting".
Infertility treatment, despite using the best quality embryos, can only manage to get half to implant in the womb. Even in healthy couples without fertility problems, many potential pregnancies are lost because fertilised eggs do not implant properly.
One in seven couples in the UK have problems conceiving and around 32,000 undergo IVF treatment each year. Dr Gillian Lockwood, medical director of Midlands Fertility Services, said a "significant" number of the one in four patients whose infertility remains unexplained could be affected with implantation problems.
"I think this is a very exciting development. In women with viable embryos only half actually achieve implantation. But there is a lot of difference between being able to identify what is going wrong and being able to fix it."
The findings are published in the journal Proceedings of the National Academy of Sciences. Professor Helen J. Mardon, of St Catherine's College, University of Oxford, and the Nuffield Department of Obstetrics and Gynaecology, said: "In many women, attachment and implantation doesn't happen and this is a major cause of infertility.
Prof Mardon, who led the study, said: "By understanding how this process works, we may be able to inform the development of drugs to help embryos implant properly." In order for the embryo to create a successful pregnancy, it must initially attach to the lining of the womb. Then cells from the embryo begin to invade the womb lining, eventually connecting with the mother's blood vessels and forming the placenta.
Professor Mardon said: "The embryo and womb lining talk to each other, molecularly speaking, which allows them to interact "When the embryo lands on the surface of the uterus wall, it triggers a cascade of signals in both the embryo and uterus. The resulting changes allow the embryo to invade the lining."
The Oxford team working with Professor Anne J. Ridley at King's College, London, have found two proteins that make cells in the womb lining move out of the way and allow the embryo cells to get in.
The research, funded by the Wellcome Trust and Medical Research Council, showed two proteins belonging to a family called Rho GTPases are involved.
Prof Mardon said: "We have shown that two proteins, called Rac1 and RhoA, control the invasion.
"The first stimulates cells in the womb lining to move and allow the embryo to invade and implant properly while the second inhibits this. We believe this controlled balance of the two proteins is critical for successful implantation of the embryo."
Using tissue samples taken from women with their consent and embryos donated to the Oxford Fertility Unit for research purposes, the team were able to simulate the very start of a pregnancy in the laboratory.
Prof Mardon said: "Essentially what we've done is to capture a particular stage of implantation going on in a petri dish. "The experiment mimics the stage in which an early-stage human embryo invades the lining of the womb, and allows us to dissect the molecular processes that control this critical stage of implantation."
