​Preimplantation Genetic Diagnosis 

What is IVF?

In vitro fertilization (IVF) is the joining of a woman’s egg and a man’s sperm in a laboratory dish. “In vitro” is a Latin expression that means “in the test tube”. This is where the common Arabic translation of IVF as “test tube babies” stems from.    

The more accurate Arabic translation used nowadays is “fertilization outside the body”.  IVF is usually used to help infertile couple to achieve pregnancy.

However, when fertile couples are at risk of having a baby with genetic disorder, IVF is used in conjunction with PGD in order to select the healthy embryos.   

Why is PGD important?

PGD makes it possible for couples with serious inherited disorders to reduce the risk of having an affected child.

Who might benefit from PGD?

It is most suited for parents who already have one child with a genetic problem and are at high risk of having another child with the same problem, or for parents who are known to be at risk of having a child with certain genetic disease. Also, PGD can be considered in couples who have been suffering from repeated pregnancy loss due to genetic disorders.

How is PGD performed?

Embryos are produced during IVF procedures by fertilizing an egg by a sperm in the laboratory.  Once the embryo contains 6-8 cells, one cell is removed from each embryo under microscopic guidance and analyzed for the presence of genetic disorders. A diagnosis is obtained and only the unaffected embryos are transferred to the mother’s uterus.

Is this a new technique?

The first clinical applications of PGD were reported in 1990, when the first pregnancies were obtained following embryo biopsy and sex determination by PCR (polymerase chain reaction) in couples at risk of having children with X-linked disorders. Since then, an increasing number of PGD cycles have been used; which show a rapidly increasing interest in this approach, even by fertile couples who agree to undergo IVF in order to make PGD possible. The list of genetic diseases for which PGD has been used is growing constantly.

How is the genetic diagnosis performed?

 In single gene disorders where the gene defect is known, such as cystic fibrosis, the actual gene(s) of the sampled embryo can be examined for the presence of the condition.

In cases of severe recurrent chromosomal diseases, such as Down’s syndrome (trisomy 21, which means three copies of chromosome 21), the number and characteristics of the chromosomes of the sampled embryo can be determined.

Finally, in genetic conditions where the exact gene defect is unknown, but which are sex-linked conditions, such as hemophilia, the DNA of the biopsied cell can be examined to determine the sex of the embryo and only embryos of unaffected sex are used.

Can PGD be performed for all genetic disorders?

PGD cannot be performed for all genetic disorders. In order to perform PGD, the genetic disorder must be “testable.” i.e. a genetic test- that can identify the specific mutation or change that causes the disease - should be known.

Can PGD be performed for sickle cell anemia?

Since 1999, Doctors were able to carry out PGD for couples who are both carriers of the recessive mutation of sickle cell disease (3). Pregnancy with an unaffected embryo can be achieved using in vitro fertilization (IVF) and PGD.

Embryos are produced by standard IVF, biopsy is obtained from each resulting embryo, and then DNA analysis using single-cell PCR is performed to determine which embryo carries the sickle cell mutation. Only unaffected or carrier embryos are used.

PGD can be a powerful diagnostic tool for carrier couples who desire a healthy child.

Can PGD technique be abused?

The answer is yes. Many people are worried that this technique might be used to produce a “designer baby”, where a certain gender is selected or only embryos with certain criteria are selected. As our knowledge of human genetic make-up is unravelled, people are worried that couples might use PGD to select certain criteria such intelligence, colour etc.. This issue is being debated at many forums worldwide.