What Should you Know Before Deciding About Comprehensive Chromosome Screening ( CCS ) Or Preimplantation Genetic Screening ( PGS )?
CCS or PGS is a scientific intervention that some patients may consider for a variety of reasons. This is different from Preimplantation Genetic Diagnosis ( PGD ). In PGD, the scientists are looking for a specific defect in the genetic material that has resulted in a genetic disorder in the family.
Whereas, in PGS or CCS we are checking for the amount of genetic material in the embryos. Too little or too much genetic material ( chromosomes ) can result in an abnormal or aneuploid embryo. This may result either in a failed IVF treatment or a miscarriage or a birth of an abnormal child. It is possible to use different technologies for testing embryos. Historically, we used the FISH (Fluorescent in situ Hybridisation) technique. Later, specialists developed new techniques such as array CGH (comparative genomic hybridization). Other methods are SNP ( Single Nucleotide Polymorphism ) microarray and NGS ( Next-Generation Sequencing ).
Who needs PGS or CCS?
Patients who are reflecting on pregnancy at a later age, such as over 38 years, can consider PGS or CCS. Also, patients with repeated IVF treatment or recurrent implantation failures can consider it. Sometimes, IVF treatment may fail because of a genetical abnormality in the transferred embryo. Without doing genetic testing of the embryo (or embryos), there is no way of knowing for sure it is genetically normal or not.
This is the case even if the embryo developed well and looked healthy on the day of embryo transfer. Other patients such as those with recurrent pregnancy loss or repeated miscarriages can also think of having PGS or CCS. Almost one percent of women of reproductive age may experience repeated miscarriages. This is defined as loss of three or more pregnancies.
Almost sixty percent of these early miscarriages (before twelve weeks of pregnancy) are due to genetically abnormal embryos. Hence, testing the embryos and replacing them with genetically normal embryos is necessary. It may improve the chances of such couples having a successful ongoing pregnancy and childbirth. Some patients with male factor infertility may also consider it.
Does PGS or CCS guarantee a genetically healthy child?
PGS or CCS is looking into the amount of the genetic material or chromosomes. When the cells are dividing, the genetic material should split equally between the two resultant cells. But, sometimes this might not be the case. Some cells may have a higher number of chromosomes and the other may have fewer than desired. Depending on the technology used for testing, the results have a reliability of around 97 % to 98%.
Also, it does not test for the genetic codes that are responsible for expressing different traits in the child. So, even if the tested cells have a normal chromosome number or amount of genetic material, the embryos may still carry an abnormal gene or genetic code. Sometimes, this may result in the birth of an abnormal child. So, PGS or CCS cannot guarantee a genetically healthy child.
Do I have to have antenatal screening even if a genetically normal embryo has been transferred?
Yes, as I mentioned earlier, the reliability of the results is around 97 – 98% even with the latest next-generation sequencing (NGS) technology. So, there is a chance that the transferred embryo may have tested falsely negative. So, all patients having PGS or CCS are still advised to avail of the antenatal screening tests.
Do I have to take fertility drugs?
All patients thinking of PGS or CCS must go through an IVF treatment. This will involve taking fertility drugs just like any other IVF patient. You will also go through the minor surgical procedure of egg collection. Once the genetic test results are available then you will go through the embryo transfer procedure. So, you will go through all the steps and processes of an IVF treatment cycle. Your specialist will discuss all the pros and cons of the treatment before you decide to go for PGS or CCS.