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The endometrium and embryo implantation

BMJ 2000; 321 doi: (Published 25 November 2000) Cite this as: BMJ 2000;321:1301

A receptive endometrium depends on more than hormonal influences

  1. Andrew W Horne, fellow, Medical Research Council,
  2. John O White, reader in reproductive biochemistry,
  3. El-Nasir Lalani (, professor of molecular and cellular pathology
  1. Department of Reproductive Medicine and Science, Imperial College School of Medicine, London W12 0NN
  2. Department of Histopathology, Imperial College School of Medicine

    How embryos attach and implant remains a mystery. Implantation represents the remarkable synchronisation between the development of the embryo and the differentiation of the endometrium. As long as these events remain unexplained, improvement in the success of in vitro fertilisation treatment and the development of contraception that modifies implantation is likely to be difficult.

    In most animals, the endometrium undergoes a series of changes leading to a period of uterine receptivity called the “window of implantation.” Outside of this time the uterus is resistant to embryo attachment. In a study by Hertig et al in 1956, women were asked to record their menstrual pattern and dates of unprotected intercourse before they had a hysterectomy for benign gynaecological disease.1 With their informed consent, their uteruses were carefully examined after operation, and the authors found that a number of them had conceived just before surgery. In these cases, embryos found in the uterus before the 20th day of the menstrual cycle were “free lying”—that is, …

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