PREIMPLANTATION GENETIC SCREENING (PGS)
In normal humans (no genetic defects) or known as euploidy, the number of chromosomes in a cell are 46 chromosomes or 23 pairs of chromosomes consisting of 23 chromosomes from sperm cells (male) and 23 chromosomes from eggs (female). Twenty-two pairs of chromosomes (44 chromosomes) are the same autosomal chromosomes in both men and women. The last pair of chromosomes (the 23rd chromosome) is the sex chromosome which determines sex. Women have XX sex chromosomes and men have XY chromosomes. If there is a deficiency or an excess in the number of these chromosomes, it is called aneuploidy. Excess chromosomes (more than 46 chromosomes) are called trisomics. While the lack of chromomon (number of chromosomes less than 46) is known as monosomics. In general, aneuploidy will lead to implantation / pregnancy failure, recurrent miscarriage, blighted ovum or if an embryo develops in the mother’s uterus it will produce a child with physical or mental defects.
WHAT IS PGS?
Pre-implantation Genetic Screening (PGS) is a technique in IVF to detect whether there is an abnormal number (excess / deficiency) of chromosomes including knowing the gender (sex chromosomes) before the embryo is transferred into the mother’s uterus so that it can increase the success rate of IVF (pregnancy rate) and reduce the incidence of miscarriage and birth of babies with genetic defects.
PGS is recommended if the mother’s age is over 35 years because of the high risk of producing embryos with genetic disorders (aneuploidy). PGS is also recommended for couples who have a history of repeated failed IVF cycles, miscarriage or have a family history of genetic defects
BIOPSY METHOD AND ANALYSIS
Embryo biopsy (taking a number of embryo cells) is done on the fifth day (blastocyst stage). The hole will be made in the pelucida zone (embryo shell) using a laser and then some cells in the embryo will be removed with a fine glass pipette. The cells that have been taken are then analyzed by the NGS (Next Generation Sequencing) method to determine whether there are excess or lack of chromosome numbers. After that the embryo will be frozen because it takes about 1-2 weeks to analyze embryonic cells. The embryo will be heated again and immediately transferred to the mother’s uterus when the results of the chromosome analysis have come out and are stated
RISK AND LIMITATIONS
There are several risks and limitations that must be known by patients:
- An embryo cannot be biopsied because no embryo has developed into a blastocyst (the embryo is not growing well)
- At the time of biopsy there is a possibility that the embryo (usually an embryo of poor quality) will become lysis / die from a fragile shell
- At the time of freezing – thawing there is a probability of embryo lysis / death around 10% (stored at -196oC)
- At the time of analysis of embryonic cells, genetic analysis errors can occur called a mosaic. Mosaic cell is a condition where one cell has genetic material that is different from other cells so that it can cause bias / not represent the real situation in the embryo. For this reason, we suggest that prenatal examinations of amniotic fluid continue in every post-PGS pregnancy.
- Another risk is that if there is a genetic defect / aneuploidy, it is not recommended for embryos to be implanted in the mother’s womb. This method cannot convert an embryo with aneuploidy (genetic defect) to euplodi (normal).
- Not all genetic defects can be detected with PGS because some genetic defects are caused by very specific genes. Some genetic disorders that can be detected are Down Syndrome, Edward Syndrome, Turner Syndrome, Klinefelter Syndrome, Jacob Syndrome, Patau Syndrome, and other major genetic syndromes. In genetic defects caused by highly specific genes such as thalassemia major or genetic defects caused by non-specific genes such as autism cannot be detected by this method. For genetic defects caused by genes that are very speciﬁc, it is advisable to carry out the PGD (Preimplantation Genetic Diagnosis) method or genetic examination in parents before PGS is performed.
- There is a possibility of machine error which results in illegible / incorrect results (1-2%)
RESULTS AND DECISIONS OF EMBRIO TRANSFERS
The results of the PGS analysis whether the euploid embryo (normal) or aneuploidy (genetic defect) including the sex of the embryo will be delivered to the patient. The decision to transfer the embryo to the mother’s womb was decided by a married couple after discussing it with the doctor.
ALTERNATIVE AFTER PGS
Prenatal examination is recommended after a post-PGS pregnancy. Examinations such as CVS (Chorionic Villi Sampling), amnioncentesis, blood tests and ultrasonography is highly recommended. Various possibilities can be further discussed with doctors and geneticists.
All PGS funding including costs for embryo biopsy, NGS analysis, embryo freezing and heating and embryo transfer will be borne by the patient. Patients must pay before PGS is done. Payment will not be returned even if the embryo results are declared abnormal / not in accordance with the expectations of the couple.
We accept the use of the embryos with the following conditions:
- If a husband or wife or both parties dies, the frozen embryo will be destroyed.
- If a divorce occurs, the frozen embryo will be destroyed.
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