| An inability to establish or maintain pregnancy is most | | | | implantation can, with appropriate consent, be |
| often attributed to lethal genetic defects of the | | | | donated for medical research. This would help to |
| embryo. For infertile couples and carriers of genetic | | | | alleviate the current lack of stem cells which are |
| disease, the option of in vitro fertilization (IVF) can | | | | needed to develop future treatments for inherited |
| often offer the only viable alternative. Over the last | | | | disease. |
| 15 years, advances in molecular genetics has allowed | | | | PGD has clear advantages but the process is not |
| for embryos to be genetically screened prior to | | | | without limitations. Many studies indicate that it has |
| implantation. Employing various genetic techniques | | | | little or no effect for mature (age 40+) women |
| such as Polymerase Chain Reaction (PCR), | | | | trying to conceive. Also, since PCR and FISH usually |
| Fluorescence in situ Hybridization (FISH) and | | | | analyze single cells, there is a possibility of false |
| Comparative Genomic Hybridization (CGH), this | | | | positive and false negative results - errors which are |
| process - known as preimplantation genetic diagnosis | | | | usually due to multiple cell lines in the early embryo |
| (PGD) - is now used to identify embryos with a | | | | through disjunction at mitosis. Consequently, healthy |
| range of genetic abnormalities such as chromosomal | | | | embryos are occasionally discarded as aneuploidic |
| aneuploidy, single gene defects and X-lined disorders. | | | | before they have the opportunity to 'self-correct', a |
| This article will discuss some advantages and | | | | phenomenon known to occur in these so called |
| disadvantages of using this technology in IVF assisted | | | | 'mosaic' embryos. |
| reproduction. | | | | Other limitations of PGD include failure to detect rare |
| The use of PGD ensures that only healthy embryos | | | | types of polygenic disease, such as those of cystic |
| are implanted in the womb. This presents a number | | | | fibrosis which has over 1000 known mutations. Even |
| of obvious advantages. Firstly, it substantially | | | | the basic cell extraction is in itself technically |
| increases the chance of successful pregnancy by | | | | challenging. The embryo must be held in position by a |
| eliminating genetic factors which cause subsequent | | | | holding pipette, while the zona pellicuda is breached |
| miscarriage. It also avoids the trauma of multiple | | | | using a micro-needle before a single cell can removed |
| terminations following unfavorable prenatal diagnoses | | | | by aspiration. This is a delicate process which poses a |
| - a reality that is all too common for couples with | | | | risk of irreversible damage to the developing embryo |
| genetic disease. Ultimately, as well as diminishing | | | | and requires considerable training. Coupled with the |
| emotional and financial stress of repeated IVF cycles, | | | | fact that the process is expensive and therefore not |
| PGD ultimately prevents the birth of individuals with | | | | available to everyone, it is clear that there are also |
| genetic disease. These individuals would otherwise | | | | disadvantages. |
| face a myriad of medical and social problems which | | | | PGD may give couples with genetic disease the |
| would both reduce their quality of life and significantly | | | | opportunity to produce healthy offspring but the |
| reduce their life expectancy. | | | | technologies have potential applications which society |
| The application of PGD to IVF presents other | | | | may deem ethically questionable. For example, is it |
| favorable opportunities. Albeit controversial, embryos | | | | morally or ethically sound to 'edit' which children |
| can be screened for histocompatibility to identify a | | | | should be born into the world? Will genetically |
| match for a sick sibling. This can often be the best | | | | affected embryos always be used in the manner for |
| opportunity - or indeed the only opportunity - to | | | | which consent is given? Should PGD be used for |
| save the life of the sibling with a terminal illness, | | | | non-medical reasons such as selection for desired |
| although this may often present ethical and moral | | | | traits or gender? These are questions that society |
| considerations. Furthermore, embryos rejected for | | | | must surely address as this technology develops. |