Pre-Implantation Genetic Diagnosis (PGD)
The technique of pre-implantation genetic diagnosis (PGD) allows for the diagnosis of certain genetic disorders of the embryo before the embryo is transferred into the uterus for implantation. Only the normal and non-pathological embryos that are not the carriers of a genetic disease will be selected for in utero embryo replacement.PGD will also minimize the risks of spontaneous abortions and provide gender pre-selection for your future baby.The American Reproductive Health Center chooses the most advanced Micromanipulation System for ICSI, PGD and other biotechnologies.
The technique is achieved by performing IVF; embryos are cultured and grow in laboratory for three (3) days to an eight cell stage. this time, a small opening is made in the zona pellucida (human eggshell); one of the cells of embryo (blastomere) is gently removed by a suction micropipette Please see the following figures for the sequence of embryo blasomere biopsy. The removed cell is then fixed to a slide and sent for genetic analysis. At present, it is possible to test for certain common chromosomal disorders (e.g., chromosomes 11, 13, 15, 16, 18, 21) as well as gender determination (chromosome X or Y).
Other genetic tests for heritary genetic diseases and gender selection are also available. It takes about 24 - 48 hours to obtain the diagnosis while the embryo is still maintained in a culture dish. When the embryo is confirmed free of genetic diseases, the embryo is then transferred to the uterus.
Time of PGD
Generally PGD (genetic testing including gender determination) is performed 3 days after egg retrieval. If Indicated, PGD is done when embryo is at 8-cell stage, typically 3 days following fertilization. The results of PGD will be obtained in 24 - 48 hours.
- Obtain numerous oocytes by ovarian stimulation and ovulation induction.
- In vitro fertilization of those oocytes by ICSI.
- Perform biopsy on the 3rd day after ICSI, at this time the embryo is at 8-cell stage (blastomeres). Please refer to the figures below.
- Genetic analysis of those cells.
- In utero embryo transfer on the fifth day after ICSI, the embryos are not a carrier of the abnormal genetics under investigation.
Genetic Study of Embryo
According to specific indication of PGD, genetic study of embryo will be performed by cytogenetic analysisor molecular technique.
- Cytogenetic analysis allows the research of numerical (polyploidies, trisomies, monosomies,) or structural chromosomal abnormalities (translocations) by the Fluorescent In Situ Hybridization (FISH) technique. After biopsy, the blastomere is lysed on a slide in order to maintain an intact cell nucleus. Specific DNA probes are then hybridized on different chromosomal regions in which we can test the presence of abnormal chromosome and the number of copy.
- Molecular analysis by Polymerase Chain Reaction (PCR) technique allows the research of mutations that affect particular genes. Specific gene regions in the genome of the biopsied blastomere are amplified to obtain a quantity of genetic material that is analyzable by molecular genetic techniques.
Indications of PGD
A. Cytogenetic indications: 1. Altered parental karyotype: (a) numerical abnormality: sexual aneuploidies, like 47,XYY (b) structural abnormality: reciprocal or Robertsonian translocation 2. Sex diagnosis for severe X-linked diseases 3. Advanced maternal age (> 38 y/o): aneuploidies, like trisomy 21 4. Multiple spontaneous abortions and repeated IVF failures
B. Molecular indications: Severe monogenic diseases (cystic fibrosis, ß thalassaemia, sickle cell anaemia, fragile X syndrome, myopathies, etc.) Each abnormality must be primarily examined to test the feasibility of the analysis by preimplantation genetic diagnosis (PGD).