Is it true that 3G IVF affects the quality of blastocysts?
Blastocyst is the ultimate stage of in vitro embryo culture and the stage at which human embryos are implanted into the mother. Blastocysts are more mature than cleavage stage embryos and are better suited to grow in the uterine environment.
In case of third generation IVF, when the blastocysts are ready, the doctor will need to biopsy the embryos in order to select good quality genetic embryos, which will increase the patient’s chances of conception, improve the live birth rate, reduce the risk of multiple pregnancies, and save the cost and time of IVF.
Many people will have this question: the embryos are already very fragile, and if some of them are taken out for testing, will it cause any harm to the embryos?
Will PGD/PGS affect the quality of blastocysts?
First of all, we need to know that embryo biopsy is to check where the embryo is? Blastocyst, i.e. the embryo formed by the fertilised egg when it develops to 5~6 days, consists of inner cell mass, blastocyst cavity and trophoblast ectoderm.
①Endocell mass, a compact mass of cells, this is the part that will develop into the main body of the foetus in the future;
(ii) Trophoblast, the circle of cells surrounding the blastocyst, which is the part that will develop into the placenta;
(iii) Blastocyst cavity, the blastocyst has an expanded cavity called the blastocyst cavity;
On the 5th and 6th day of blastocyst, the number of cells in the embryo has increased significantly and can reach more than 100.
While biopsy is a microscopic extraction of 1-2 trophoblast cells for genetic screening.
Since the endoderm cells (which will develop the foetus in the future) are not touched, this is to avoid damaging the quality of the blastocyst.
All blastocysts will be frozen and stored during the embryo delivery period until the chromosome results are available and those that pass the test can be selected for transfer.
The blastocysts are still alive after the cells are removed and their nature will not change, let alone affect the future health or fertility of this embryo.
What is PGS?
PGS is also known as Preimplantation Genetic Screening.
PGS is an examination of all the chromosomes of the embryo, and it can observe whether the chromosome pairs are missing or not, and whether the chromosome morphology and structure are normal or not.
However, PGS can only screen at the chromosome level and cannot examine genes.
PGS can detect chromosome number problems. The chromosomes of a normal embryo exist in pairs, i.e. they are all diploids. If there is only 1 or 3 chromosomes on a particular number, then this is a chromosome number problem.
Common ones are trisomy 18 and 21, Turner’s syndrome, Koch’s syndrome, etc.
PGS can also detect chromosome structure problems. Each chromosome has multiple gene segments and if the position of these gene segments is altered then it is also difficult for this embryo to develop properly.
Some of the common ones are chromosomal balanced translocation, Roche translocation and chronic granulocytic leukaemia.
What is PGD?
PGD is Preimplantation Genetic Diagnosis of embryos
PGD determines whether an embryo carries a mutation in a gene, which is a segment of DNA on a single chromosome, that may cause a specific disease.
PGD can only find out whether a disease-causing gene is carried or not, but cannot alter or repair it and has limitations.
PGD is mainly used to address genetically inherited diseases. They are genetic diseases caused by 1 or more pairs of allelic deletions or aberrations. There are thousands of single-gene genetic diseases, such as colour blindness, progeria, haemophilia, albinism and retinoblastoma.
Common single-gene genetic diseases, such as thalassaemia and progressive muscular dystrophy.
What is PGT?
In 2018, the World Health Organisation merged PGD and PGS and united them under the name of pre-implantation genetic testing, or PGT for short.
Compared to the S (screening) in PGS and the D (diagnosis) in PGD, the T in PGT stands for testing, which is also more accurate and rigorous.
PGT-A: Pre-implantation genetic testing for aneuploidy.
PGT-A is able to screen the number of chromosomes and get embryos with normal chromosome number, which provides a reference standard for embryo transfer and a higher live birth rate for embryo transfer!
Suitable population:
PGT-A is suitable for the vast majority of patients undergoing IVF treatment. This is because all women can produce chromosomally abnormal embryos, and the probability of chromosomally abnormal embryos increases significantly with the woman’s age, regardless of the number of embryos.
PGT-M: Preimplantation genetic diagnosis of single-gene disorders.
PGT-M is usually able to test the embryo for the gene responsible for a specific disease, for example, in cases where both parents are carriers of the gene responsible for the disease (haemophilia, albinism, etc.), the probability of the offspring suffering from the disease is as high as 25%!
Suitable population:
①Patient and partner are carriers of the same autosomal recessive disease (e.g. cystic fibrosis).
(ii) The patient is a carrier of an X-linked disorder (e.g. Duchenne muscular dystrophy).
(iii) The patient or partner has an autosomal dominant disorder (e.g. Huntington’s disease).
④ The patient or partner has mutations associated with hereditary cancer syndromes (e.g. BRCA1 and 2).
⑤ The patient has a child or is pregnant with a single gene disorder.
⑥ The patient wants to be HLA-matched.
PGT-SR: Pre-implantation genetic testing for chromosomal structural rearrangements.
PGT-SR is a test for chromosome structural and numerical abnormalities before IVF embryo implantation in cases where one or both parents are known to have a certain chromosomal disorder, due to their high risk of having children.
Suitable Population:
Chromosomal balanced translocations.
Roche translocation.
Inversions, etc.