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Updated April 16, 2007

This page will explain and illustrate how the egg cell is fertilized and how the early pregnancy attaches itself to the womb. A link between the new life(embryo) and its mother will be formed. Implantation is the establishment of this link between the mother and the embryo.

We will also discuss the phenomena known as implantation bleeding.

The egg cell is released by one of the ovaries and than sucked into a fallopian tube. The lining on the inside of the fallopian tube is also a highly specialized mucus membrane. The cells on the surface of this mucus membrane contain specialized hair like protrusions which is constantly moving in such a way that there is a constant movement of fluid from the ovary towards the opening of tubes and from there toward the cavity in the womb. This movement causes a suction effect. Anything in the vicinity of the ovaries ( like the egg cell) will be sucked into the womb. Refer to Normal Ovary.

An interesting fact is that fertilization does not occur in the womb , but at the opening of the tube near the ovary. That sperms swim all the way from the vagina, through the womb and upstream through the fallopian tubes.

After fertilization the fertilized egg cell is slowly sucked through the fallopian tubes into the cavity of the womb. It only arrives in the womb about five days after conception. The egg than attaches itself to the endometrium ( the lining on the inside of the womb.).

The drawings in the next section ( further down) will illustrate the whole process.

We will also discuss implantation bleeding. Implantation bleeding should not be confused with bleeding during pregnancy. We regard real implantation bleeding as a bleeding episode that occurs two weeks after conception ( four weeks after the previous menstruation), but more about it near the end of this page.

The discussion continues slightly further down the page.

Illustrations of the process of Implantation
The first illustration gives an enlarged view of the process of fertilization, see Fertilization. It shows a schematic representation of fertilization and the movement of the fertilized egg through the fallopian tube.

The sperms are schematically represented by the small red structures. The red dot represents the head and the red line the tail.

The yellow-brown sphere represents the egg cell.

Fertilization is illustrated in the entrance to the fallopian tube. A sperm attaches itself to the egg cell. It penetrates the egg cell while discarding its tail.

The egg is now fertilized and we changed its appearance to a purple sphere.

The green arrows indicate how it(the fertilized egg) is moving through the fallopian tube towards the uterine (womb) cavity.


The next set of drawings will give a simplified overview of how the egg cell attaches itself to the endometrium and while growing bigger buries itself in the endometrium.
The fertilized egg cell arrives in the womb. The little ball represents the fertilized egg.
The fertilized egg (or embryo) attaches itself to the endometrium (the lining on the inside of the womb).
The embryo is dissolving the endometrium. In plain terminology it is digging a hole in the endometrium to bury itself in the endometrium. The next and the following drawings shows an enlarge view of this process.
You see a yellow structure bulging from the ball penetrating the purple line. The purple line represents the surface of the endometrium and the yellow structure represents a structure that is formed by the embryo. This structure is called the trophoblast and is going to infiltrate and dissolve parts of the endometrium including blood vessels. The blood in the infiltrated blood vessels will than be diverted into spaces within the trophoblast. The developing embryo will than later obtain its oxygen and nutrients from this diverted blood.
The placenta ( after birth) is going to develop from the trophoblast.
The yellow structure is larger and invading a maternal blood vessel. The blood filled cavities are visible within the yellow structure(trophoblast).
The trophoblast (yellow structure) is larger and invading another blood vessel. As it is growing it pulls the embryo (the little ball) deeper into the endometrium. The mother's blood is diverted into cavities in the trophoblast.
The trophoblast continues to enlarge and to infiltrate deeper into the endometrium, pulling the ever enlarging embryo with it.
The changes occurring inside the embryo are not shown or discussed here.
The process continues and the embryo is nearly completely implanted (buried) in the endometrium.
The surface (purple line) is also growing back and beginning to cover the embryo.
The embryo is fully implanted and covered by the surface epithelium of the endometrium (the purple line representing the surface completely covers the embryo and trophoblast.) The trophoblast continues to grow and invades more blood vessels.
This drawing illustrates a phenomenon known as implantation bleeding. Maternal blood fills the cavities in the trophoblast. The trophoblast surrounds the whole embryo and just before it is completely covered some of blood in the superficial cavities might leak into the uterine cavity and escape via the vagina. This implantation bleeding occurs exactly at the time of the expected menstruation. It therefore can cause uncertainty about the duration of pregnancy. Implantation bleeding seldom occurs. Implantation bleeding varies from being scanty to a near normal menstruation but is usually less and of different shade than a normal period.

Remember it is not a common phenomena.

It should not be confused with other causes of bleeding in early pregnancy. It is one of the causes of bleeding in early pregnancy, but most cases of early pregnancy bleeding are not implantation bleeding.

Not everybody shares our view, and some doctors do not believe that implantation bleeding really occurs. We believe it does, but to diagnosed it as such, it must occur at the time of the expected menstruation. The pregnancy is then four weeks more advance than expected.

See Implantation for more information about implantation bleeding.