SCIENTISTS have identified why some embryos fail to implant in the womb, a discovery which could lead to new treatments for infertility.

The British research has found the mechanism by which embryos become attached to the womb lining.

Professor Helen Mardon of the Nuffield Department of Obstetrics and Gynaecology and St Catherines College, University of Oxford, who led the study, said there could be implications for fertility treatment.

"In many women, attachment and implantation doesn't happen and this is a major cause of infertility," Prof Mardon said.

"By understanding how this process works, we may be able to inform the development of drugs to help embryos implant properly."

During implantation, cells from the embryo begin to invade the womb lining, eventually connecting with the mother's blood vessels and forming the placenta.

The Oxford team, along with Professor Anne Ridley at Kings College, London, identified molecules responsible for controlling the invasion of human embryo cells into the womb lining.

They found two proteins belonging to a family called Rho GTPases are involved.

These proteins ensure cells in a small area of the womb lining move out of the way to allow cells from the embryo to invade.

"We have shown that two proteins, called Rac1 and RhoA, control the invasion," Professor Mardon said.

"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.

"If the balance of the Rho GTPases is altered, the cells of the womb lining don't migrate and the embryo doesn't implant."

The findings are published in the journal Proceedings of the National Academy of Sciences.