Pre-implantation Genetic Diagnosis (PGD)

Pre-implantation genetic diagnosis or PGD is a technique of preventing certain inherited conditions from being passed on to a couple's child. The process involves a thorough checking of the embryo's genes during an IVF cycle.

When is PGD recommended?

This procedure is recommended under the following conditions:

• The couple has had abortions in the past because the baby was found to have a genetic condition
• The couple has a child or family history of serious genetic conditions

What does PGD test for?

The embryo can be tested for more than 100 genetic conditions using PGD. If the genetic conditions mentioned in the above section are considered sufficiently serious, the clinic may be permitted to check the embryo for that condition.

What clinics can offer PGD?

Clinics offering PGD need to have a specific license to do so. The license lets the clinic test an embryo for any single condition or combination thereof that is considered serious enough. Some clinics may be experienced in testing certain genetic conditions more than others.

Risks of PGD

The risks associated with PGD testing are the same as those of a conventional IVF cycle, but there are some additional risks like those given below:

• The embryos may get damaged during the cell removal process
• The testing may not be fully conclusive or reliable

The procedure

The procedure for Pre-implantation genetic diagnosis usually involves seven steps that are given below:

1. A conventional IVF cycle begins and the eggs are retrieved and fertilized by the male partner's sperm

2. The fertilized eggs are separated and placed in incubation. They develop into embryos, which are place in the lab for 48-72 hours until they reach the eight-cell stage.

3. The embryologist then removes a cell (blastomere) or two from the embryo

4. The cells undergo genetic testing to see if the embryos to which they belong contain the genetic condition(s) in the couple, couple's family, or couple's child.

5. Embryos that do not have the condition are separated. Some are transferred to the uterus for development

6. Other unaffected and separated embryos are cryogenically frozen for later IVF cycles. Embryos that have the genetic condition perish.

7. The woman undergoes a pregnancy test two weeks after the embryos are transferred

In some cases, the embryos may be allowed to grow for five-six days, at which point they will each have 100-150 cells that either form the placenta (trophectoderm) or the fetus (inner cell mass). Cells are removed from the trophectoderm without harming the embryo, which helps in getting more accurate results.

The chances of successful pregnancy after PGD

Lack of data associated with PGD makes it difficult to assess success rates, but most couples using this procedure do it because they want to avoid their child from suffering a genetic disease, and not for any fertility problem. Success, of course, depends on a lot of conditions like the woman's age and the cause of infertility, if any. Sometimes, there may not be any embryos suitable for transfer after PGD because:

• All of them had the genetic disease
• Removal of cells damaged the embryos
• Not enough embryos were available