PGD

In order to select the embryos with the greatest potential for their subsequent transfer to the uterus in an In Vitro Fertilization (IVF) cycle, at Provida Fertility Clinic we have at your disposal the most advanced methods to discard genetic anomalies such as Down's Syndrome.

Preimplantation genetic diagnosis (PGD) is a method of analysis used in conjunction with in vitro fertilization (IVF) and allows only embryos free of genetic and chromosomal abnormalities to be transferred to the mother's uterus.

PGD is indicated for couples at risk of transmitting genetic diseases, as well as those with a history of recurrent miscarriages and implantation failure after several IVF cycles. Similarly, it is recommended for women over 35 years of age and men with sperm meiosis disorders (where sperm have extra or fewer chromosomes).

There are several techniques to analyze the chromosomes of an embryo for genetic diseases. The most common, called FISH, allows only 12 of the 23 pairs of chromosomes in each cell to be analyzed and is not fully accurate. The microarray technique, on the other hand, makes it possible to determine the complete chromosome composition of an embryo in a single cell and it's accuracy falls between 96 and 98 percent.

The transfer of tested embryos by microarray to a receptive uterus increases the probability of having a baby to 60 to 70 percent.

What is preimplantation genetic diagnosis (PGD)?

From the age of 35, a woman's fertility decreases considerably and her chances of forming embryos with an unfavorable genetic load increase. In order to select the embryos with the greatest potential and help you realize your dream of having a baby at home, at Provida Fertility Clinic we have at your disposal the most advanced methods of preimplantation genetic diagnosis (PGD).

Preimplantation genetic diagnosis (PGD) is a method of analysis complementary to in vitro fertilization (IVF) that selects only embryos free of chromosomal abnormalities to be transferred to the mother's uterus, where they can continue their development normally.

PGD is performed on the third day of embryonic development, when the embryo has approximately eight identical cells or blastomeres, each containing all the genetic information that could constitute the individual.

In order to carry out the preimplantation genetic diagnosis (PGD), it is necessary to perform an embryonic biopsy, which consists of making a small opening on the surface of the embryo, through which a micropipette is introduced, aspirating from one to 15 cells, without affecting the development of the embryo.

At Provida Fertility Clinic the procedure is performed by highly qualified specialists, allowing the embryo to continue its development as if the cell had never been removed.

Once the cell is obtained through micro manipulation techniques, with the PGD technique a genetic analysis is performed to determine if an embryo contains the normal number of chromosomes that should be present in human beings.

Before carrying out the embryo transfer it is necessary to wait 48 hours for the results of the analysis and allow the embryos to develop to the blastocyst stage in the laboratory. This facilitates the selection of embryos of higher quality and with greater implantation power.

• The purpose of PGD is to identify genetic and chromosomal alterations in embryos and it is indicated for:
• Couples at risk of transmitting chromosomal disorders.
• Couples with a history of recurrent miscarriages, which may occur due to an imbalance in the number of chromosomes.
• Couples with implantation failure after several IVF cycles.
• Men with alterations in the meiosis of the spermatozoa, that is to say, in those who have more or fewer chromosomes.
• Women over 35 years of age.

One of the major advantages of PGD is that it is performed before the embryo is transferred to the uterus and, unlike methods such as amniocentesis, it does not carry the risk of miscarriage or force the parents to consider the difficult decision to terminate the pregnancy if an unfavorable diagnosis is obtained.

Preimplantation genetic diagnosis (PGD) also makes it possible to determine the sex of the embryo. This is medically relevant because it prevents the transmission of gender-specific congenital diseases such as hemophilia, muscular dystrophy, cystic fibrosis and Huntington's disease.

The success rates of an In Vitro Fertilization (IVF) cycle with PGD are higher than the success rates of IVF without the use of this method because preimplantation genetic diagnosis (PGD) makes it possible to discard genetic conditions that may increase the likelihood of recurrent abortions.

Also, transferring only normal embryos maximizes the chances of implantation, pregnancy and having a baby at home regardless of the woman's age.

How are the embryo's chromosomes analyzed?

Two of the techniques used to analyze the chromosomes of the embryo are

1. FISH method

The most common procedure is called fluorescent in-situ hybridization (FISH). It currently analyzes only 12 of the 23 pairs of chromosomes in each cell, so it is not accurate.

Even when FISH reveals that all of the chromosomes tested are normal, there is a nearly 50 percent chance that there are abnormalities in the chromosomes that were not tested. Another disadvantage of FISH is that in many cases a single cell is not enough for the study, so the results will be limited if the aspirated cell is not of the necessary quality.

Due to the inaccuracy of FISH, it is necessary that it be carried out on the fifth day of embryonic development (blastocyst phase) in which the embryo has about one hundred cells and it is possible to remove and analyze several of them without damaging it. It is important to note that after blastomere aspiration on the fifth day of embryonic development, it is necessary to vitrify the embryos to await the results of the test before transferring them, which may compromise their viability and increase the cost of treatment.

2. Microarray method

The process of analyzing embryos has become much simpler and more accurate thanks to a new technology known as microarray, which makes it possible to determine the complete chromosome composition of an embryo (23 pairs of chromosomes) in a single cell obtained on the third day of embryonic development. Before using this method it is necessary to subject the DNA sample obtained from the blastomere to a specialized amplification process in which billions of copies of the DNA are created. This is known as WGA and few laboratories in Mexico have the technology to perform it.

Once enough DNA is available, it is checked against a control sample for losses and gains of chromosomal material. The procedure consists of marking both DNA samples with fluorophores of different colors and placing them in a microarray, that is, in a glass plate impregnated with DNA sequences contained in localized points with well-defined coordinates.

Each DNA sequence or fragment represents sequences of the chromosomes in the cell. It is therefore possible to determine how many copies of each chromosome are present by looking at the number of particles of each color that are present at each coordinate of the microarray.

By analyzing all the chromosomes in the cell, the microarray technique can identify diseases such as Down syndrome with 96 to 98 percent accuracy. In turn, the transfer of embryos analyzed by microarraying a receptive uterus increases to 60 to 70 percent the probability of obtaining a healthy newborn.

Although the microarray technique favors the birth of healthy individuals and is available as a research tool in a large number of laboratories.