Embryo Implantation in the Uterus

Following fertilization, the zygote undergoes multiple divisions, forming a cluster of cells known as a morula. Around days 4–5, the morula further develops into a blastocyst, which consists of an outer layer of cells (trophoblast) and an inner cell mass (the embryonic precursor).

The embryo moves into the uterus, where it attaches to the uterine lining (endometrium), marking the beginning of pregnancy. This process, known as implantation, is essential for pregnancy to continue and typically occurs around 6–10 days after fertilization.

Factors Involved in Implantation

Successful implantation requires several key steps, beginning with the preparation of the uterine lining. Under the influence of the hormone progesterone, the endometrium thickens and secretes nourishing mucus, creating an optimal environment for embryo reception. The blastocyst typically attaches to the upper part of the uterus.

Trophoblast cells from the embryo begin secreting enzymes that help it penetrate the surface layer of the endometrium. The uterine lining must be adequately prepared for implantation, meaning it must be of appropriate thickness and nutrient rich. Hormonal support is crucial, with progesterone and estrogen playing key roles in preparing the uterus.

The immune system plays an important role, as the mother’s immune system must accept the embryo, which is genetically half foreign to her body. Furthermore, for successful implantation, the embryo itself must be healthy, meaning it must be genetically normal and viable.

Implantation is a critical phase for the success of pregnancy. If the embryo does not attach properly, the pregnancy will not progress. A successful implantation enables the embryo to receive nourishment and facilitates the development of the placenta.

At Dextra Fertility Clinic, embryos in IVF (in vitro fertilization) treatments are almost always cultured to the blastocyst stage before transfer or freezing. This approach increases the likelihood that only viable embryos are transferred to the uterus or frozen for later use. Preimplantation genetic testing ensures that the embryo is chromosomally normal before transfer.