An embryo that has reached the age of 5 days already has about 30-60 cells, so they are more hardy and have a higher potential for implantation into the endometrial mucosa. It is noted that the percentage of successful pregnancies is much higher, namely, when a five-day embryo is transferred. It is known that embryos at the crushing stage can carry genetic defects in about 60% of cases, and at the blastocyst stage only in 30% of cases, since most of the “defective” embryos do not live up to 5 days. Therefore, the probability of selecting more successful embryos and increasing the chance of getting a pregnancy is much higher if the human embryos are used at the blastocyst stage. The disadvantage of this method is the separate development of the embryo and endometrial mucosa up to 5 days, which may be the reason for the termination of the division of embryos.
The procedure of embryo transfer to the blastocyst stage is identical to that on days 2 and 3. A woman who is on the gynecological chair is inserted into a sterile thin catheter into the uterine cavity through the cervical canal, and embryos are inserted through the catheter. Usually, 2 embryos are planted to avoid multiple pregnancies.
Thus, we see that replanting embryos at the blastocyst stage gives a higher chance of obtaining the desired pregnancy.