Repromed is the first – and only – clinic in SA to offer Preimplantation Genetic Screening (PGS) on site. This means there are no lengthy delays to getting your test results during already stressful time. It allows IVF scientists to confirm the correct genetic material (number of chromosomes) is present in an embryo being transferred. The presence of extra or missing chromosomes is known as aneuploidy and may explain an embryo’s failure to establish or maintain a pregnancy. PGS may assist couples with;
- repeated IVF failure
- recurrent miscarriage
- a known chromosome rearrangement (known as a chromosome translocation)
- gender selection for a medical reason
Aneuploidy
Most cells in the human body have 23 pairs of chromosomes – one copy of each pair is inherited from the mother and the other copy is inherited from the father. The first 22 pairs of chromosomes (referred to as autosomes) are numbered from 1 to 22, and are arranged from largest to smallest. The 23rd pair of chromosomes are the sex chromosomes. Females normally have two X chromosomes (XX), while males normally have one X chromosome and one Y chromosome (XY). Aneuploidy occurs when the cells that make up our body divide but the chromosomes do not separate evenly between the two cells. This means the cells have an abnormal number of chromosomes (either too many or too few), which in the embryo can result in genetic disorders in children or result in miscarriage during pregnancy. If there is an error in division of the egg’s chromosomes and one of the pairs of chromosomes fails to separate, the egg or embryo will have an uneven number of chromosomes. In Down’s syndrome, for example, the embryo has a total of 47 chromosomes instead of 46 because it has three copies of chromosome 21 instead of the normal two copies. This kind of chromosome error, in which one of the chromosomes has three copies instead of the proper two copies, is called “trisomy.”
All of these chromosomal errors, including trisomies, monosomies, and various combinations can occur in virtually any of the chromosomes, and these errors, as a group, are called “aneuploidy.” These numerical chromosomal errors in a cell can be diagnosed by embryo screening. The ageing process of eggs makes it harder for them to undergo normal chromosome separation. This leads to an increase in genetic abnormalities in resultant embryos, even though these embryos may appear normal on visual assessment. Studies have shown that rates of aneuploidy are increased in older women.
Screening for aneuploidy before an embryo transfer increases the likelihood of selecting the embryo(s) with the best chance of implanting while also reducing the rate of miscarriage or chances of a pregnancy of a baby with a genetic condition.
The screening test is available to at-risk couples, and is able to screen all 23 pairs of chromosomes to ensure only embryos with a normal chromosome complement are selected for transfer. The test is able to measure whole chromosome copy imbalances, as well as specific structural chromosome rearrangements, from a single embryo cell.
How is the screening performed?
During an IVF cycle, patient’s embryos are assessed for biopsy on days 5 or 6. During biopsy a single cell or cells are removed from the embryo. Following the embryo biopsy, embryos are cryopreserved and the testing is performed on the biopsied cell(s). The screening is performed in-house in the Repromed laboratories.
Only embryos that develop normally in culture are able to be tested for genetic abnormalities, and only embryos that have progressed and are both viable and genetically normal after the biopsy are suitable for transfer. Unfortunately, in some cases there will be no suitable embryos for screening, or no genetically normal embryos following screening, and embryo transfer will not take place. However following the screening, patients are able to have euploid (normal) embryos transferred in a frozen embryo transfer cycle.
How does maternal age influence aneuploidy?
Chromosome aneuploidy (abnormal number of chromosomes) is a major cause of IVF failure, pregnancy loss, and in rare cases abnormal pregnancy and live birth. Most aneuploidies arise in the final stages of egg development and increase exponentially with maternal age. The percentage of aneuploid embryos is known to increase with maternal age, however, it may occur in embryos from couples of all ages.
What are the success rates?
A recent randomised prospective IVF study has shown that selectively implanting euploid (normal) embryos following screening with PGS can increase pregnancy rates by up to 65% (Yang et al, 2012. Molecular Cytogenetics).
It is important that each couple has their individual risk assessed by a fertility specialist before determining if PGS should be incorporated into their IVF treatment plan.
Please call Repromed on (08) 8333 8111 or fill out the enquiry form below, if you need further information on our PGS technology.