Culture to Blastocyst

Culture to Blastocyst

The goal of Assisted Reproduction is to obtain a singleton pregnancy. The best way to avoid a twin pregnancy is to transfer only one embryo. The optimum stage to transfer a single embryo is at the blastocyst stage. Sequential culture of an embryo to a Day 5 blastocyst stage embryo is a more advanced evolutionary phase of development and given that there are a greater number of differentiated cells, the embryo of the highest quality can be selected and transferred, increasing the chances of pregnancy.

Who should transfer at blastocyst stage?

The transfer at blastocyst stage is apt for patients who have obtained a high number of good embryos after an IVF cycle or egg donation. This permits nature to select the strongest embryos and consequentially the best embryos are then transferred. It is also recommended when pregnancy has not been achieved after a few Day 3 transfers.

A single embryo transfer is increasingly recommended, especially in women over 40 using donor eggs in their treatment.

What advantages does a transfer at blastocyst stage have?

In a natural pregnancy, fertilization takes place in the Fallopian tubes and the embryo develops and rolls down the tube towards the uterus. On the fifth day of development, now at the blastocyst stage, the embryo reaches the uterine cavity. On Day 6, implantation in the endometrium occurs.

For an IVF cycle to simulate a natural conception as closely as possible, embryo transfer is recommended at this moment. Moreover, if a laboratory embryo reaches Day 5, it is considered to be a good embryo with implantation potential. This means that blastocyst transfers have higher implantation potential, and therefore, transfers on Day 5 increase implantation possibilities.

Sequential culture to blastocyst permits selecting, out of all the embryos, those with the highest quality and greater potential for implantation.

cultivo a blastocisto en España

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The stages of embryo development

cultivo de blastocisto
cultivo de blastocisto
cultivo de blastocisto
cultivo de blastocisto
cultivo de blastocisto

On Day1 of embryo development, we can see if fertilization is completed. The egg that is correctly fertilized has two pronuclei and two polar bodies. The two pronuclei, one from the mother and the other one from the father correspond to their genetic material. These structures will disappear and between 25-27 hours, cellular division begins. At this moment, the embryo is made up of two cells.

We can observe cellular division 43-45 hours post-insemination. At this stage, the embryo should have 4 cells.

Until Day 3, the embryo uses the genetic material of the egg. On this day, the embryo will begin to use its own genetic material, which makes this moment extremely important for the embryo. The embryo should have divided into 8 cells,
Up until Day 3, embryologists assess the symmetry of the cells, the percentage of fragmentation and the number of nuclei that each cells has. The important thing is that each cell should contain a single nucleus.

On Day 4, the embryo is at the morula stage. All the embryonic cells join and form a single mass where the cells cannot be distinguished one from another. The structure looks like a blackberry. At this stage, embryologists cannot evaluate embryo quality.

This is the blastocyst stage. The external cell layer or trophectoderm will become the placenta and the inner cellular mass will become the future baby. At this stage, cells will not be evaluated individually but together as the trophectoderm and the inner cellular mass. . This is the last phase before hatching and implantation in the uterus.

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