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Fertilized eggs implanted late may not survive

Copyright © 1999 Nando Media   (http://www.nandotimes.com)
Copyright © 1999 Agence France-Press
June 10, 1999

BOSTON  - Researchers have found that human eggs implanted more than 10 days after fertilization are less likely to survive than fresher ones, according to a study published Thursday in the New England Journal of Medicine.

National Institutes of Health researchers said fertilized eggs implanted on the ninth day had a 13 percent of being miscarried. One day later, the risk rose to 26 percent, according to the study of 221 women.

The risk of loss jumped to 52 percent if the egg was implanted in the uterus on the 11th day, and to 82 percent thereafter, the researchers said.

The NIH researchers could not determine why late uterine implantation resulted in miscarriages, but speculated that the late eggs were imperfect.

"The uterus may be receptive to pregnancy only during a limited time-window, shutting out defective embryos that get there too late," they said.

A previous study in 1998 by NIH found that a quarter of all fertilized eggs failed to survive six weeks after fixing to the uterine wall.