The PGD is an alternative of prenatal diagnosis to identify genetic and chromosomal anomalies before implantation or conception of the embryo, favoring the establishment of a pregnancy free of the condition in question.

The procedure is performed on the fertilized eggs obtained with the ICSI procedure before transferring them to the maternal uterus. After fertilization, the cleavage of the egg gives rise to a pre-embryo consisting of two cells. Subsequent divisions of each of them will give rise to 4 cells, then 8 and so on over the course of the days. The cells of the embryo are called blastomeres. All blastomeres, in a normal development, should be identical to the genetic constitution determined at the time of the fecundation of the gametes. Therefore, with the study of one of the blastomeres one can know the genetic constitution of the embryo. Because approximately 40% of the fertilized eggs are stopped before the 3rd day, it is not advisable to perform the embryo biopsy before the 3rd day, and only in those that have reached the development of 8 cells, to make sure that the study is carried out in viable embryos, since more than 80% of the pre-embryos that have developed 8 cells on the third day, development continues. The biopsy on the 5th day at the blastocyst stage has the advantage over that of day 3 in that one makes sure that the biopsied pre-embryo is potentially transferable, because the rate of embryogenicity in humans rarely exceeds 50% . In addition, since on day 5 more cells can be removed to study, it gives greater possibility of achieving a diagnosis. As soon as the trophoblast biopsy is performed, each blastocyst is vitrified individually, and when the genetic results are available, we will know which are the transferable ones. It is advisable to transfer one at a time, because the possibility of twinning is increased in IVF procedures. The transfer in a deferred cycle to the stimulated one may or may not be done with the preparation of the endometrium with estrogen and progesterone physiologically.

The PGD is appropriate for couples who have already had a child affected by a genetic or chromosomal disorder, and who are at greater risk to have other affected children. It is required to know if the genetic problem is due to a chromosomal cause or to a specific gene mutated molecularly characterized. Another requirement is that the couple is fertile or infertility is reversed with the Vitro fertilization procedure. When the mutation has not been characterized, the study could be performed by linkage analysis.
When the disorder is linked to sex (to the X chromosome) and the mutation has not been characterized, the couple could benefit from the sex selection of the pre-embryos transferring only the female sex.

In addition, the PGS screening of pre-embryonic aneuploidies could be useful for those couples who have experienced repeated spontaneous pregnancy losses of chromosomal origin, such as those who have performed several failed IVF / ICSI in vitro fertilization procedures.

The PGS could be beneficial for women over 35 who wish to achieve a greater chance of developing pregnancy with IVF / ICSI procedures, because the rate of oocytes with aneuploidy increases with the age of the woman. The oocytes are always the age of the woman, since they begin to form in the intrauterium life and are stopped before the end of the first division. In contrast, sperm do not have the age of the male, because they form continuously in adult life. However, several studies have revealed that aneuploidy rates worsen when the male has severely altered semen. Therefore, the PGS could also be beneficial for those couples who must resort to the ICSI procedure for severe male factor.
Currently there is clear evidence of the beneficial value of PGD for couples with increased genetic risk for gene and chromosomal diseases. In contrast, the PGS would seem to be beneficial for couples of good prognosis, which are those that produce a sufficient number of embryos. Couples with poor response to ovarian stimulation could collect blastocysts with several cycles of ovarian stimulation.
It can also be beneficial in people with greater predisposition to develop hereditary tumors. Also it might be beneficial for a sibling who needs to be transplanted with bone marrow, accessing the couple to an HLA typing as well as for women with Rh or group Kell negatives, highly sensitized, to prevent the transfer of the embryos Rh or Kell positives.

Although there is the possibility of recovering the embryos originated in the maternal womb with uterine washes, it is advisable to obtain them with in vitro fertilization procedures.

Furthermore, to minimize the risk of contamination with parental and / or extraneous cells, the ICSI procedure is recommendable, where the operator injects only one sperm in each of the ova, devoid of granulosa cells and washed.

The woman must receive hormonal medication so that several follicles can mature. Later the mature follicles are punctured to recover the oocytes of its interior

The oocytes and semen are processed before performing the ICSI procedure. The fertilized oocytes are normally kept in culture for three days.

To obtain the blastomere from the clived embryo or several cells of the trophectoderm of the blastocyst is necessary to make a drilling in the pellucid zone (ZP).

The drilling of pellucid zone can be done in several ways:

1) Mechanics: trying to cut  a portion of the ZP with a micropipette

2) Chemistry: trying to dissolve a portion of the ZP  with an acid-Tyrode solution

3) With Laser: doing some laser shots modulated through the optical system of the microscope. We prefer the latter method because in a single step it allows aspiration of the blastomere and above all because it is considered more innocuous for the survival of the embryo.

Prior to the biopsy, the embryos are placed in a suitable medium to loosen the cell junctions. Subsequently they are placed each one of them in microdrops under oil perfectly labeled. With the help of the micromanipulative microscope, the embryo that is going to be biopsied is placed in the center of the field and it is focused with the objective of 400 increases which allows the passage of the laser beams. The blastomere that is to be aspirated is selected by positioning it at time 3 and it is fastened to the embryo at hour 9 with a holding  pipette.

The cell that is chosen must have a single nucleus. According to the size of the cell, one or two 15-millisecond laser shots are practiced in the ZP adjacent to the blastomere to be extracted. Once the area has been drilled the pipette is inserted and the blastomere is gently aspirated until it is removed. When a trophoectoderm biopsy is performed, it is preferable to perforate the ZP on day 4 and obtain part of the trophoectoderm that is hatching.

When the disorder is chromosomal the genetic study can be realized with fluorescent in situ hybridization technique (FISH), comparative genomic hibridization (CGH)  or quantitative fluorescent PCR (QF-PCR). On the other hand, if the disorder is genic, it will be analyzed by minisequencing or by linkage analysis.

The Fecunditas Preimplantation Diagnosis program has been in existence since 1999. The Institution has a Genetics laboratory in which all types of genetic studies can be carried out at the chromosomal and gene levels. Therefore, it offers PGD in patients at risk to have children with dominant, autosomal recessive gene disorders and those linked to the X. To carriers of reciprocal translocations, Robertsonian or inversions. Also for HLA typing, RhD incompatibility, Kell group and predisposition to certain familial tumors. For elderly women and men with male factor Screening of Aneuploidies (PGS or PGT-A) by molecular karyotyping.

In addition, the Evaluation of Reproductive Genetic Risk is carried out:

• Karyotyping in peripheral blood
• Karyotyping of meiotic chromosomes
• FISH in semen
• DNA fragmentation in semen
• Study of segregation patterns in carriers of balanced chromosome rearrangements
• Mutation sequencing
• HLA typified

Genetic Counseling: for those who require it.

First of all it should be emphasized that the preimplantation genetic study, whether carried out in a blastomere on the third day of development or in several cells of the trophoblast at the fifth day, is still a screening method, because the cell extracted on the third day or the various cells on the fifth day are more likely to be cells that make up the placenta, the chorionic villi and extraembryonic tissues, rather than the embryo. The blastocyst transferred in the uterus takes ten days to nest and, once implanted, embryonic differentiation begins. Therefore, the constitution found may not correspond to that of the future embryo-fetus-born. Of all the available prenatal techniques, the only one that is diagnostic is that performed in amniocytes from amniotic liquid. Blastomere or trophoblast biopsy would be equivalent to chorionic villus puncture, which, although used as a prenatal diagnostic test, has a 98% diagnostic certainty.

The diagnostic uncertainty can not only be due to technical or biological limitations, but also to human errors and, within human errors, the most frequent is due to the relationships without contraception, either in fresh or deferred cycle. There are other limitations related to the technique of the procedure such as complications during DNA amplification, potential contamination with exogenous DNA and other technical difficulties.

Not always that a PGD is performed the transfer of non affected embryo is guaranteed, because all were abnormal or because they were not embryogenic. It is important, therefore, before accessing the procedure to predict the possibility of finding normal embryos according to the genetic disorder and the ovarian reserve of the woman. In general, this type of diagnosis requires a normal response to ovarian stimulation and that the oocytes are embryogenic. For recessive disorders 3 out of 4 embryos are potentially transferable, for dominant 1 in 2, for reciprocal translocations 1 in 5, for Robertsonins 1 in 4 and for HLA 1 in 4.

All types of biopsy are invasive, therefore they are recommended when there is an increased risk that justifies it, although in the preimplantation period there is no teratogenic risk, due to the effect of all or nothing of the injuries, but when they affect all the blastocyst cells could be cause of not implantation.