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Implantation of the Embryo

Reviewed by Stephen Willis, MD
Implantation of the Embryo

Implantation occurs when the early-stage embryo attaches to the lining of the womb, and connects to the mother’s blood vessels to form the placenta. Unsuccessful implantation is the leading cause of infertility in young women.


Process of Implantation

 

The fertilized egg divides to form an early-stage embryo called the blastocyst. The blastocyst travels to uterus for implantation. Successful implantation requires intimate interaction between the trophoblastic cells of the embryo and the cells of the endometrium at the molecular level. Implantation occurs only during the “window of receptivity” that spans from the 20th to the 24th day of the menstrual cycle. The selectin, integrin and trophinin molecules on the surface of the endometrium and trophoblastic cells form bonds, which promote the invasion of the uterine cavity by the trophoblastic cells. After implantation occurs, the embryo is nourished by the lining of the uterus, until the placenta develops and attaches to the growing embryo. The body also starts producing human gonadotropin (hCG), a hormone that is essential during the early stages of the pregnancy. The pregnancy tests you take at home detect the presence of this hormone in the blood.


Implantation Bleeding

 

Implantation occurs without any apparent signs. A positive pregnancy test is the best indication of successful implantation. Some women may also experience implantation bleeding. Implantation bleeding typically lasts for one or two days with a flow that is much lighter than a normal menstrual period. The bleeding begins 10 to 14 days after conception when implantation occurs. A small amount of blood leaks out of the uterine lining as the trophoblastic cells invade it. Many women may also confuse implantation bleeding with menstrual bleeding and panic.


Bleeding and spotting that is similar to implantation bleeding may also occur in women during ectopic pregnancy. These types of pregnancies are not viable as the fertilized egg grows in the fallopian tube, and may, in fact, be dangerous to the mother. It is, therefore, best to consult a doctor if you observe any changes during pregnancy that concern you.


Problems Associated with Implantation

 

Inflammation or infection of the uterine lining is one of the main causes of unsuccessful implantation in women. Many women with fertility issues actually suffer from repeated implantation failures. Other causes of implantation failure include reduced blood flow to the endometrium as well as resistance of the endometrial lining to the hormone estrogen. Hormonal imbalance in women can also lead to unsuccessful implantation. Some experts also believe that improper development of the embryo can also prevent implantation.

In such cases, the fertilized egg reaches the embryo and leads to a miscarriage. Most women at this stage are unaware of their pregnancy.

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