The method of in vitro fertilization (IVF) implies the fertilization of a woman's oocytes with the sperm of a man and the further cultivation of embryos for 5-6 days outside the female body . The embryological stage ends with the transfer of embryos into the uterine cavity or their cryopreservation. In this case, embryos are selected with the highest probability of their implantation into the uterine wall, which means pregnancy.
Stages of development of embryos
The embryonic (embryonic) period is the period of development of the embryo from the moment of conception to the ninth week of pregnancy. The first week of embryonic development is called the preimplantation period, since the embryo is able to exist and develop in a nutrient medium without physical contact with the mother's body. This period ends with the implantation of the embryo into the wall of the uterus (endometrium), which contributes to the further development of the embryo.
The preimplantation period includes the following stages of embryo development:
Day 0: fertilization of the egg with sperm.
1st day: the formation of a zygote - a unicellular embryo with a double set of chromosomes, formed as a result of the fusion of the maternal and paternal genetic material.
2nd day: cleavage - the stage of development at which the embryo begins to divide without increasing in size. In this case, the embryo develops only thanks to the maternal genetic material stored in the egg.
3rd day: also includes a crushing stage. Moreover, the more synchronously the division of blastomeres occurs, the greater the likelihood of a favorable outcome. By the beginning of the third day, for normal further development, the embryo should consist of 6-12 cells. Also on this day, compaction begins - the process of forming bonds between the blastomeres of the embryo. This process is due to the activation of its own genetic material. Such a multicellular embryo with emerging intercellular connections is called morula.
4th day: crushing and compaction processes continue. In this case, a cavity begins to form inside the embryo.
5th day: the formation of a blastocyst - the stage of development of the embryo, in which two types of cells are distinguished: some will subsequently form a fetus, others will form the baby part of the placenta. The growth of the embryo at this stage is due to two processes - an increase in the number of cells and the volume of the blastocyst cavity.
6-7 days: the embryo leaves the protective membrane to be implanted into the endometrium.
After implantation of the embryo into the endometrium, the content of hCG in the mother's blood begins to increase. That is why, to diagnose pregnancy, a blood test is taken on the 14th day after the embryo transfer.
