Pre-transfer genetic diagnosis (PGD), which has recently started to be applied within the scope of IVF treatment, allowed patients or carrier couples to have healthy babies. Embryos, obtained by the fertilization of eggs with sperms during the IVF treatment, can be examined via one or two tissue (blastomere) samples to detect the presence of several familial and chromosomal diseases before they are placed into the uterus.
Even if they do not have infertility problems, couples with chromosomal or genetic diseases can undergo IVF treatment and obtained embryos can undergo a subsequent PGD procedure so that such couples can have healthy children. The PGD procedure is carried out by collecting 1 or 2 tissue samples from the embryos, which are obtained by the fertilization of the eggs from the mother by the sperm from the father during an IVF treatment cycle and, then, by placing embryos into the mother's uterus after confirming that those embryos are healthy.
The PGD method is mostly recommended for disorders; which are inherited via familial transmission and impossible to be treated in the baby after birth. The first PGD baby was born in the US in October 2000. That pregnancy was achieved by the transfer of a single healthy embryo; which was selected out of about 15 embryos examined via the PGD method.
The PGD method has been used in the US and Europe since the 1990s and is currently applied in our clinic when indicated. PGD can be recommended for patients with a history of recurrent miscarriages, unsuccessful in vitro fertilization attempts, advanced age, or genetic or chromosomal diseases in one of the partners (the presence of the disease in one of the spouses or one of the spouse is a carrier). Using the PGD method, healthy embryos and the ones that are not the carriers of genetic disorders are selected and transferred. For example; ornithine carbamoyltransferase (OTC) deficiency; which is an X-linked disorder transmitted by the mother to the baby resulting in a liver disease,can be avoided by selecting the non-carrier embryos out of the embryos obtained via assisted reproduction techniques and transferring them into the mother's uterus.
Today; several diseases including hemophilia, muscular diseases such as Duchenne muscular dystrophy and neuromuscular dystrophy, Tay-Sachs disease, cystic fibrosis, sickle cell anemia, and some other chromosomal diseases such as fragile X syndrome and Down syndrome can also be diagnosed with the PGD method.
The PGD method is applied without any harm to the embryos and its result can be obtained within 2 weeks. This method can be performed as follows:
- Polar body biopsy obtained from egg cells (oocytes) (can only detect maternal diseases)
- Tissue sampling (blastomere biopsy) from three-day-old embryos (embryos with 6-8 cells only) (This is the most commonly used method in routine practice)
- Tissue sampling (blastocyst biopsy) from 5-day-old embryos. Today; the array CGH method is used for genetic diagnosis. Thus, the numerical structure of all of the 46 chromosomes in humans can be revealed.
There is continuous research in order to detect genetically transmitted diseases such as cardiovascular diseases, diabetes, hypertension, and cancers by using the PGD method, aiming to avoid and finally eliminate such diseases in next generations.