Couples who undergo in vitro fertilization (IVF) treatment will have to be examined for their medical history as a way to determine what IVF protocol and medications are best suited for their IVF treatment. Couples who have been found with a history of serious genetic diseases possess a possible risk of passing their genetic disorder to their children. To avoid such circumstances, a technique is used before implants are made. Preimplantation Genetic Diagnosis (PGD) is used to eliminate the risk of genetic disorder transmission.
PGD and How it Works
Preimplantation Genetic Diagnosis (PGD) is another way of prenatal diagnosis which avoids selective pregnancy termination or abortion. PGD is used to determine genetic disorders in embryos before they are implanted to the uterus. It allows the couples at risk to conceive a healthy baby and avoids possible termination of a fetus that possesses a genetic disorder. PGD has identified many monogenetic disorders but has yet to determine other forms. A single gene disorder or a chromosome which has an abnormal structure or number causes genetic disorder. With PGD, it can examine actual genes of a sample embryo if it is a single cell disorder. Other genetic disorders only affect male, an example for this is haemophilia.
Normal PGD and IVF technique is applied if the procedure needs Fluorescence in situ hybridization (FISH) analysis. If there is abnormality in the semen, Intracytoplasmic Sperm Injection (ICSI) or polymerase chain reaction (PCR) analysis is required. In PGD and IVF technique, a single cell is taken out from an 8 cell embryo through an opening in the outer protective layer. The cell is then observed with a microscope and is analyzed if there is an existence of a genetic disorder.
Three methods of PGD and IVF Technique
- Fluorescence in situ hybridization (FSH) analysis - In this method specific chromosomes are indentified with the use of fluorescent probes that are specified for chromosomes. The fluorescent probes bind only to those parts of the chromosome which show sequence of similarity and can be visualized by a fluorescent microscope. It is able to detect X, Y, 13, 18, 21 chromosomes in a single cell at the same time and can determine sex linked diseases and also abnormal structure and number of chromosome.
- Polymerase Chain Reaction (PCR) - It is a method which amplifies DNA fragments that were selected and removed from the nucleus and detects the mutation of a gene. A diagnose can be obtained within the day. The embryos that were unaffected are replaced either on the 4th or 5th day into the uterus.
- Haplotyping - This method utilizes DNA profiling in identifying chromosomes which carry abnormal genes.
Comparative Hybridization: A New Technique for Diagnosis
PGD and IVF technique can only analyze few pairs of chromosomes and there is a tendency to miss other abnormalities in the embryo. A new technique known as comparative hybridization can identify 23 chromosome pairs but this technique still needs more scientific proof for it to be applied in IVF treatment. For couples who have consistently failed in pregnancy and intend to use PGD and IVF should be advised of the consequences of misdiagnosis and no diagnosis when the embryos are being tested.