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Embryos go through several stages of development. In the first stage, called the germinal stage, there are 4 different phases: fertilization, cleavage, blastulation and implantation. Transferring an embryo before it reaches the blastocyst stage holds certain risks. Waiting until this stage offers several theoretical advantages in the process.

After an egg is fertilized, it begins to divide into multiple cells. The large single celled zygote begins to divide into smaller cells. During this phase, there is no increase in mass as the cells begin to multiply. Cell division occurs every 18 – 20 hours. If the cell division is too fast or too slow, it may indicate a chromosomal or metabolic defect. When the blastulation phase is reached, the embryo is transferred to the woman’s womb.

Advantages of Blastocyst Transfer

The blastocyst phase of embryonic development is a more advanced stage. When an embryo has matured to this point, it is more likely to result in a pregnancy. Another advantage of blastocyst transfer is that it allows the embryologist to select the most viable embryos for transfer. It can also decrease the number of embryos that are transferred, reducing the chances of multiple births. There is also better synchronization between the embryos and endometrium at the time of the transfer.

Even though this may be ideal for most women, it is not suitable for everyone. Women who are above the age of 35 may have a better chance of pregnancy with a day-three embryo.


One of the main risks involved in blastocyst transfer is a possibility that there will not be any embryos that advance to this phase. This could happen if there are genetic abnormalities or if the embryos cannot tolerate the artificial culture system. When this is the case, embryos transferred on the third day after fertilization may be better. This can only be predicted if there has been a previous IVF.

Neway Fertility helps people build their families. Our fertility specialists will consult with you to determine your needs and the most effective treatment to help you start your family. Contact our office today to schedule a consultation appointment.

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