Since the study of produced embryos in vitro revealed a high rate of chromosomal aneuploidy. Most types of aneuploidy are not compatible with life, regarding these most common syndromes caused by non-sex chromosome aneuploidy including Down syndrome, Edwards syndrome, and Patau syndrome. Aneuploidy is usually not inherited and can involve any chromosome. In addition, the embryos that derived from advanced reproductive age mothers have significant incident of chromosomal mutation. Therefore, such embryos have reduced potential for achieving a viable pregnancy that lead to the implantation failure and spontaneous miscarriage, consequentially the relative low success rate observed during IVF treatment.
Chromosomal aneuploidy can cause distinct over 50% of spontaneous miscarriages with include birth defects of embryos. The risks of having a child with abnormal chromosome have been increasingly observed with maternal age. Couple who are at increased risk for having aneuploidy embryos should consider using PGS testing. These groups of individuals include:
• Women over 35 years of age
• Couples who have experienced several spontaneous miscarriages of unknown cause
• Couples with several cycles of IVF that have not achieved pregnancy
• Men with low sperm concentration
• Couples with a previous pregnancy with chromosomal abnormality
PGS using for normal chromosomal embryos selection in these couples greatly reduces the risk of miscarriage and increases reproductive success.
Using preimplantation genetic screening to selective normal implant embryos can help.
1. Improves implantation rates : Abnormal or aneuploid embryos will fail to implant into a woman’s uterus. Therefore using PGS diagnosis for normal chromosomal embryos before transferring can increase the implantation rate.
2. Reduced spontaneous abortion : Several studies has been discovered miscarriage is often caused by de novo abnormalities in chromosome number or aneuploidy. Since PGS could evaluate the numerical and aberration changes in chromosome and large imbalance of chromosome, consequentially the abnormal embryos will not be transferred. Therefore, PGS reduces the risk of miscarriage especially in high risk groups.
3. Increases ongoing pregnancy rate
4. Enables single embryo transfers, decreasing the number of high-risk multiple pregnancies
Preimplantation genetic screening (PGS) has played an important major role in assisted reproduction technology which is related to the detection of chromosome abnormalities in embryos with the goal of improving the outcome of IVF for several decades. Beside the common aneuploidy, the other inheritance of chromosomal abnormalities has been addressed to the abnormal of structural chromosomal rearrangement including translocations, inversions and duplications/deletions. In addition, some chromosomal abnormalities such as aneuploidy is possible for PGD by using the fluorescence in situ hybridization (FISH) in biopsied blastomeres so far.
Moreover the commercial probes was available for the X and Y chromosome detection for gender determination, and other developed protocols were introduced the multicolor-FISH to screen up to five chromosomes simultaneously. Although FISH has been used for PGD but new molecular genetic techniques has recently replaced the FISH method for aneuploidy screening including array comparative genomic hybridization (aCGH), single nucleotide polymorphism (SNP) arrays, quantitative PCR (qPCR).