Preimplantation Diagnosis

Preimplantation Diagnosis techniques enable the study of genetic characteristics of the embryo before its implantation in the womb.

The diagnosis is made in the first stages of embryonary development, after a cycle of "in vitro" fertilization. With the help of a micromanipulator, the embryonary biopsy is performed, which consists in the removal of one or two cells (blastomeric) of each embryo for analysis.

During the diagnosis process, the embryos are kept in culture until the results are obtained, and only normal embryos will be transferred.

There are a series of gender-related illnesses, especially related to the “X” chromosome, which are transmitted by women but only affect men, such as Hemophilia and Duchenne Muscular Dystrophy. Thanks to the preimplantation diagnosis techniques, it is possible, in those cases, to prevent the birth of affected boys, transferring only female embryos.

The identification of cell gender through the biopsy is performed through Fluorescent in situ Hybridization (FISH), which consists in the application of specific probes for each type of chromosome, enabling the visualization of the "X" and "Y" chromosomes in different colors.

With this technique, it is also possible to diagnose some numerical changes, such as trisomy of 21, 13 and 18 chromosomes and aneuploidies of  "X" and "Y".

In patients over 35 years old subjected to assisted fertilization there is an increased risk of embryos carrying chromosomal anomalies (such as Down syndrome). In these cases, it is possible to study embryos before their implantation and to verify if they are chromosomally normal.

Literature has shown that Preimplantation diagnosis can also be performed in cases of autossomic illnesses (genetic-originated, independently from the sexual chromosomes) using Molecular Biology techniques.

In these cases, embryonary biopsy is performed and the gene that causes the change is, then, detected, through the use of Polymerase Chain Reaction (PCR) technique, which allows the selection of unaffected embryos. This technique can be applies in the cases in which the gene and the correspondent specific DNA sequence are known, such as the case of Cystic Fibrosis.