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Infertility & Reproduction Health Center

New Clue to Common Infertility Cause

Embryos Stick to Uterus With Help of a Protein
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Jan. 16, 2003 -- A new discovery about what makes a week-old embryo attach to the uterus may one day help diagnose and treat early pregnancy loss and infertility. Failure of the embryo to implant itself on the wall of the uterus is responsible for about three-fourths of lost pregnancies, according to researchers.

But a new study in the Jan. 17 issue of Science suggests that a reaction between the embryo and uterus occurs soon after fertilization and is responsible for creating a sticky environment that allows the embryo to attach and begin the first stages of implantation.

Until now, researchers say, little has been known about the initial stages of embryo implantation and what might cause an embryo to fail to adhere to the uterine wall.

Researchers found that molecules on the surface of the embryo interact with molecules on the mother's uterine wall about six days after fertilization to make a sticky environment and slow the embryo's progress along the uterine wall.

"It's like a tennis ball rolling across a surface covered in syrup," says researcher Susan Fisher, PhD, of the University of California, San Francisco, in a news release. "The embryo's journey along the uterine wall is arrested by the sticky interaction."

Once the embryo comes to a rest and adheres to the uterus, it can establish a nourishing blood supply from the mother through the placenta.

Researchers say laboratory tests found that the outer surface of the early embryo makes a protein known as L-selectin at the same time in the menstrual cycle when the uterus becomes enriched with carbohydrates and is most receptive to implantation. This protein binds with carbohydrate, which creates the stickiness.

Researchers say the same sticky interaction is known to help disease-fighting cells adhere to areas of inflammation.

By learning more about what causes the embryo to adhere or fail to attach to the uterine wall, researchers say they may be able to develop tests that can pinpoint causes of infertility and diagnose if a woman is capable of becoming pregnant. Researchers at UCSF say they've filed a patent for use of L-selectin for this purpose.

SOURCE: Science, Jan. 17, 2003 • News release, University of California, San Francisco.

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