Implantation Window

Definition - What does Implantation Window mean?

An implantation window refers to the period of time in which the uterus is ready to receive the blastocyst for implantation. This window lasts about 2-4 days and is the only time that the embryo can implant in the uterus. It is essential that an embryo implants in the uterine wall for it to continue developing and go on to become a successful pregnancy.

The implantation window is also called endometrial receptivity or uterine receptivity.

FertilitySmarts explains Implantation Window

In most successful pregnancies, implantation occurs 8-10 days after ovulation. The first step of implantation is called adplantation. In this phase, the hatched blastocyst adheres loosely to the endometrium during the implantation window. It will later roll to a nearby site of the uterus where it will firmly attach.

Uterine receptivity is not well understood, but the hormones estrogen and progesterone are known to play a key role in readying the uterus for implantation. Estrogen causes the cells of the endometrium to divide and multiply, while progesterone halts this process and creates a stable environment within the endometrium for implantation to occur. Conditions, such as endometriosis, affect the thickening of the endometrium and can therefore interfere with implantation.

The implantation window occurs on days 20-24 of the menstrual cycle. If a woman is undergoing treatment with assisted reproductive technology (ART), implantation occurs about 1-5 days after blastocyst transfer.

The embryo must sufficiently implant at this time so that hormones are released to inform the body of a pregnancy. If this does not occur, the next menstrual cycle will begin and the woman will miscarry. If the embryo contains a major genetic error, it will often not develop or implant properly, also causing an early miscarriage.

Once successfully implanted, the placenta will begin to form to help support the embryo, and later the fetus, in development.

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