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Infertility Cubby

Thinking About PGD
by Chelsey Langland

It may be that you've, sadly, had one or more miscarriages. Or you've had an IVF cycle or two fail. Or, you know that you or your partner carry a genetic anomaly. For any of these reasons, you might consider utilizing the technology that will allow the embryologist to perform a preimplantation genetic diagnosis (PGD) on your embryos, before they are transferred. While nothing can substitute for a visit with your RE, who knows your particular circumstances, this article will be an attempt to introduce the concept.

PGD is done after the IVF cycle (with or without ICSI) has produced embryos. A few days after fertilization, a couple of cells are pulled off the embryo and examined, and the genetically normal embryos are then available for transfer. PGD is done for a number of different reasons. Some of these include:

A known genetic abnormality in one of the parties who will be contributing either eggs or sperm. For example, a woman may have a chromosomal translocation, where bits of her genetic information have become entangled. This can result in the embryo receiving either too much or not enough genetic material, and the embryo that is formed is often not able to survive past the early stages of gestation. With PGD, embryologists are able to make special probes that can detect the translocation, resulting in the ability to transfer only genetically normal embryos.

This technology works for other diseases for which there is a known genetic component, including some types of muscular dystrophy, cystic fibrosis, and Huntington's disease. At some facilities, if the parent knows that he or she could potentially be a carrier, but they are unsure of their own status, the lab can perform PGD and create normal embryos without disclosing carrier status to the parent.

PGD is also useful for screening out certain X-linked diseases, such as certain types of muscular dystrophy. PGD can ensure that only female embryos are transferred. It is important to note here, however, that avoiding X-linked diseases is an entirely different enterprise from using PGD for non-medical gender selection. While using PGD for family building is theoretically an option, not every facility is willing to allow the use of PGD technology for this reason. Using PGD for gender selection is somewhat controversial, and is a value judgment that can be made only by the parent(s)-to-be.

A mother-to-be who is over 35 and using her own eggs. After age 35, it becomes statistically more likely that a woman's eggs will contain a chromosomal anomaly. Often, these anomalies are expressed as either monosomies or trisomies. An example is Trisomy 21, which causes Down's syndrome. Of much more concern are the anomalies which create lethal defects. Standard PGD (in other words, PGD used when not looking for a known genetic defect) can screen out the most common chromosomal anomalies.

Of course, many women well into their upper-30s have beautifully healthy children. However, some women want to know that they are transferring only genetically normal embryos.

A woman with multiple failed IVF cycles. It may be that you don't know of any genetic aberrations in your family, and you haven't even hit 30 yet. But you've still not had any success with IVF. PGD can be a helpful tool here, as it can give you a true picture of your embryos. This can rule out an underlying genetic cause, as well as give you an idea of your egg quality.

A woman with multiple miscarriages. Much like a woman with multiple IVF failures, a woman who has had repeated losses may want to take a look at her embryos in order to determine whether there is a genetic component to her losses.

Because PGD requires that the embryo be disturbed and sampled, it can potentially stop the embryo from properly developing. For this reason, many clinics refuse to perform PGD unless there are an adequate number of available embryos. That number varies from place to place, although six seems to be a common benchmark. If you have had instances of poor response, it may be that your RE will discourage PGD. Ultimately, this is a decision for you, your partner, and your medical team. Costs vary from place to place, and can escalate if you require the creation of special probes that are customized to detect your particular genetic anomaly. Average costs seem to fall between $2,500 and $5,000. These costs are on top of the cost of the normal IVF cycle.

PGD is not about creating super-babies or hand-picking family composition. In its everyday applications, it's about giving people a shot at parenting children who share their genetics. This is vitally important to some people, and PGD is helping to make it a reality. For more information, please speak with your RE.

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