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 Friday, 17 January, 2003, 00:00 GMT
Secrets of embryo success revealed
Embryo
It is not fully understood why an embryo implants
Scientists may have found out what makes a human embryo stick to the wall of the womb and start developing.

This could create ways of improving the chances of women who have trouble conceiving.

When an egg is released at a certain point in a woman's cycle, it can be fertilised as it passes down the tube between the ovaries and the womb.

However, even if it is fertilised and starts to develop as an embryo, there is no guarantee that it will become implanted in the womb wall as it passes by.

However, the researchers, from the University of California at San Francisco, US, may have discovered a quality that makes particular embryos more likely to succeed.

It's like a tennis ball rolling across a surface covered in syrup

Professor Susan Fisher, UCSF
Some embryos, it seems, exude a sticky protein on their surface about six days after conception, which stops them in their tracks as they roll along the sides of the womb.

In turn, the womb walls will produce higher quantities of another substance that interacts with the sticky protein - but only at a point when they are ready for implantation.

Once an embryo has stopped in the right spot, it is more likely that good quality implantation will take place.

Professor Susan Fisher, one of the researchers, said: "It's like a tennis ball rolling across a surface covered in syrup.

"The embryo's journey along the uterine wall is arrested by the sticky interaction."

Right conditions

The sticky protein is called L-selectin, and researchers looking at early embryos called blastocysts - little more than a small ball of cells - found that L-selectin was produced on its exterior at the time of implantation.

They found that the uterus becomes enriched with carbohydrate at a certain point in the cycle.

L-selectin is able to briefly catch hold of these carbohydrates, slowing its descent.

The university has now filed for a patent, suggesting that the research may lead to a test which could assess how likely a woman is to fall pregnant.

Womb conversation

Dr Roger Searle, director of anatomy and clinical skills at the University of Newcastle, UK, said the study, published in the journal Science, was another piece of evidence suggesting a "dialogue" between embryo and womb lining as the two prepare to meet.

He said that both might be releasing chemical signals which prepared each other for implantation.

He said: "It's a radical idea, which is gaining more support, that the embryo is actually communicating with the uterus.

"It used to be thought that everything was down to the mother, but now it seems more likely that there is this dialogue going on."

Scientists also suggested that the finding could shed some light on pre-eclampsia, a condition in which the failure of the placenta to attach itself properly within the womb sets in train a sequence which can eventually threaten the life of both mother and child.

See also:

10 Jun 99 | Health
18 Sep 01 | Health
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