A healthy human genetic code consists of 23 pairs of chromosomes, and each of the chromosomes may contain hundreds or thousands of genes. Half of this genetic material is inherited from the mother and half from the father, and the combination creates the “blueprint” for their offspring. Unfortunately, the process does not always work seamlessly. Problems with the chromosomes or specific gene can cause a pregnancy to miscarry or result in serious genetic conditions and diseases. PGD can be used to identify these issues before a pregnancy occurs. PGD can:
In order to perform PGD, pre-embryos must be available for testing. The patient goes through a regular IVF cycle. Fertility hormones stimulate the ovaries into producing more eggs. When the eggs are mature, they are retrieved from the ovaries in a procedure performed in the clinic under light sedation. Then, in the lab, eggs and sperm are combined and fertilization occurs. The resulting pre-embryo can then be tested.
During the PGD procedure, an embryologist carefully removes a few cells from the embryo. These cells, called blastomeres, are then evaluated for abnormalities. The evaluation normally takes 7-10 days. Once all of the pre-embryos are tested, only healthy, normal embryos are selected for transfer to establish pregnancy in a later cycle.
PGD is not necessary in all cases. Your physician will advise you whether or not it is indicated for your specific situation. PGD is often recommended for:
There are many potential benefits of PGD, but like every decision you make about your fertility treatment, it requires careful consideration. For couples confronted with a family history of serious or even life threatening genetic diseases, the decision may be easy. For a patient with less pressing concerns, a review of the other benefits and the risks of PGD may be helpful.
If you have reason to believe that you will want to use PGD as a part of your IVF process, it is important to select a clinic with a strong reputation for the procedure. While PGD can be performed safely without harm to developing embryos, any handling or manipulation of an embryo carries very low risk of injury. PGD is a rapidly developing technology, and the benefits of a cutting-edge fertility laboratory and extensively experienced staff are crucial to the success of PGD and the safety of the embryo. For many couples, PGD offers them a chance to have healthy biological children that they could never have had otherwise. In the hands of an expert clinic, the benefits of PGD greatly outweigh the risk.
PGS is a technique for testing whether embryos have any problems with their chromosomes, which is thought to be the most common reason IVF treatment fails
PGS (also known as aneuploidy screening) involves checking the chromosomes of embryos created by in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI)for abnormalities.Embryos with abnormal chromosomes often end in miscarriage, a failed treatment cycle or the child may have a condition like Down’s Syndrome.During PGS, a single cell or a small number of cells is removed from the embryo. The DNA of these cells is then tested to see whether they have any chromosomal abnormalities. Only embryos without chromosomal abnormalities are placed back in the womb.
Older women are more likely to have eggs with the wrong number of chromosomes, so traditionally it’s been offered to women over 37. Abnormal chromosomes are thought to be the main reason why older women have difficulties conceiving and are more likely to have a miscarriage or a baby with Down’s Syndrome. Your doctor may also recommend PGS if you have a family history of chromosome problems, if your sperm is at risk of carrying abnormal chromosomes, or if you’ve had several miscarriages or failed IVF attempts without explanation.
In the past, some clinics recommended PGS to older women with a history of miscarriage or failed IVF cycles, men whose sperm was at risk of having chromosomal abnormalities or people with a family history of chromosome problems. However, to date there is little evidence showing it improves success rates for these groups. There have been some small clinical trials which have shown that PGS can improve IVF success rates for women under 37 with no history of miscarriage or failed IVF cycles. Until larger trials have been run and we have more evidence, there’s no guarantee that PGS can improve your chances of pregnancy
Because PGS involves removing a cell or number of cells from an embryo this can cause damage to the embryo and prevent it from developing once it has been transferred into the womb. Also research has shown that often the cells in an embryo are not chromosomally identical (called mosaicism). PGS relies on test results from one or a small number of cells being representative of the embryo as a whole. As this is not always the case, it may be possible for an embryo to give an abnormal test result when it is in fact capable of producing a healthy pregnancy.
However, PGS also has some treatment specific risks. This includes the possibility of a misdiagnosis, although modern PGS techniques are very accurate. There’s also the risk that if all the embryos are found to have abnormal chromosomes there won’t be any embryos to put back in the womb. This is especially likely for older women