It is the process in which the fertilized egg or a blastocyst gets attached to the endometrial wall of the uterus to attain pregnancy. During this stage, the embryo establishes a strong connection with the maternal circulation and starts its embryonic developmental journey.
The endometrium is receptive to a fertilized egg for a shorter period in the luteal phase which is termed as “Implantation window”. The window lasts for 4 days & follows up to 6 days after the peak of LH levels. And it is essential for the blastocyst to reach endometrium during the implantation window in order to get a successful implantation. Any delay in the blastocyst transport can cause loss of endometrial receptivity. Blastocyst Implantation occurs 6-8 days after fertilization.
In this stage, the blastocyst sheds its zona and approaches the endometrium with a particular orientation. The finger-like projections known as chorionic villi helps to bring the blastocyst nearer to the uterine epithelium. The uterine epithelium cells have glycoprotein on its surface which acts as a barrier between blastocyst and endometrium. The blastocyst uses its enzymes to digest the glycoprotein which results in interlinking of trophoectoderm with luminal epithelial cells.
Attachment occurs on 6th or 7th day post ovulation. At this stage, the strong association is established between endometrium and blastocyst. Due to enzymatic breakage of glycoprotein, the adhesion molecules (includes cadherins, intergrins, glycan, & lectin etc.) in blastocyst and endometrium have free accesses to each other.
In this stage, the embryo needs to connect with the mother for development. The blastocyst completely penetrates the endometrium by day 9. The blastocyst consists of two main components – The trophoblast & the Inner Cell Mass (ICM). The function of trophoblast cells in the embryo is to invade the endometrium to build maternal connection with an embryo. The Inner cell mass give rise to a fetus. As embryonic trophoblast makes contact with endometrium it further differentiates into two layers: Cytotrophoblast & Syncytiotrophoblast. The ICM in the embryo makes a two differentiated layers hypoblast & Epiblast. The cavity arises between Epiblast & Cytotrophoblast is known as amniotic cavity. Cells originate from hypoblast which forms a thin membrane called as exocoelomic membrane. Cells of hypoblast and exocoelomic membrane forms wall of primary yolk sac. The growth of trophoblast forms Cytotrophoblast & Syncytiotrophoblast becomes quiker at this stage. The lacunar networks begin to form in the Syncytiotrophoblast & by the 12th day the lacunar networks stops growing .The uterine blood vessels in the endometrium comes in contact with lacunar networks which directs the placental trophoblast to maternal blood circulation. Also the endometrial stroma becomes dense cellular matrix called as decidua, which afterward becomes the maternal part of the placenta.
In Assisted reproduction, the key cause for implantation failure is the hatching disability of embryo. Presently, no research is available to distinguish the embryos which have the ability to hatch and grow into a healthy embryo. No hatching is a possible reason for pregnancy failure in many elderly women. In that case, zona pellucida can be disrupted by using laser assisted hatching technique to improve the pregnancy rate. Reviva Fertility Clinic & IVF Center In Chandigarh offers all the latest techniques which can treat various types of infertility.
For more information about infertility please visit our website www.revivaivf.com