Implantation Of Human Embryo & Pregnancy


The term “implantation” is used to describe the process of attachment and invasion of the uterus endometrium by the blastocyst (conceptus). It is referred to as the stage of pregnancy at which the embryo adheres to the wall of the uterus. It helps the embryo to grow by receiving nutrients from the mother. In humans, implantation of a fertilized ovum is most likely to occur around 6 – 9 days after ovulation. In fact, this is a highly coordinated event that involves both embryonic and maternal active participation


The reception-ready phase of the endometrium of the uterus is usually termed the “implantation window” and lasts about 4 days. Initially, the newly hatched blastocyst loosely adheres to the endometrial epithelium. Then it rolls over the endometrium to find a suitable place where it gets attached firmly.

Embryo–endometrial dialogue

The first step of implantation is the formation of a fetal-maternal interface. The next crucial step is the invasion of the embryo into the endometrium. Certain molecules and pinopodes are involved in bringing embryo and endometrium together and help attachment of embryo. The embryo produces cytokines and growth factors and receptors for endometrial signal.

Does body immunity play role in successful pregnancy?

The body immune system plays an important role in the early pregnancy process. The host (mother)genetically different from the transplants(fetus), raises the possibility of a graft-versus-host reaction. The embryo, as a genetic product of both maternal and paternal chromosomal material, can be seen as an allograft to the uterus.
The immunological action against the embryo can be described as maternal restraint. 

Can we calculate Implantation period?

Implantation of a fertilized ovum is most likely to occur around 6 – 9 days after ovulation. It falls around day 21 of a regular menstruation cycle. During the female fertile age, there is an average chance of pregnancy of approximately 15% per cycle. Embryonic attachment is the establishment of pregnancy, to be proven by finding human chorionic gonadotrophin (HCG) in maternal blood. Some women may experience slight bleeding and cramping pain during this process.

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