Preimplantation genetic testing is a sophisticated technique by which the embryos are tested to identify genetic defects in them before they are transferred to the uterus.
Transferring genetically abnormal embryos (aneuploid) can lead to no pregnancy or an early pregnancy loss/ abortion or the birth of a child with physical or mental disabilities. This not only poses a physical, emotional & financial burden on the couple, but repeated abortions can lead to permanently damaging the lining of the womb and hence making the patient incapable of carrying her own child.
Preimplantation genetic testing enables the selection & transfer of genetically normal (Euploid) embryos.
There are two different categories in this technique:
1.Preimplantation genetic diagnosis (PGD):
Recommended when one or both genetic parents have a known genetic abnormality. Here the embryo is tested to determine if it also carries that specific genetic condition. This serves to prevent certain genetic diseases or disorders from being passed on to the child.
Eg: Sickle cell anaemia, Huntington’s disease, Cystic fibrosis, Thalassaemia, Duchene muscular dystrophy etc.
- Preimplantation genetic screening (PGS):
This procedure is done in couples with a normal genetic makeup but with the following history:
- Advanced maternal age (> 35 yrs),
- history of repeated pregnancy losses/abortions (either naturally or with IVF/IUI)
- Previous failed IVF attempts
- Infertility due to severe male factor (very poor semen analysis report).
- If previous pregnancy has been affected by any chromosomal abnormality
How is it done?
- Preimplantation genetic analysis requires the woman to go through the standard IVF cycle to create embryos
- The embryos thus created in the laboratory are then biopsied. Embryo Biopsy involves microsurgical removal of one or few cells from these IVF embryos.
- The DNA of these cells is then evaluated to determine if their genetic content is normal or if they possess the inheritance of a problematic gene
- Though embryo biopsy is much preferred at the blastocyst stage (day 5). It can also be done at the cleavage stage embryo (day 3)
- Following the biopsy, the embryos can be frozen or continue to grow in the lab till the genetic analysis report is available.
- Embryo transfer is done with a single genetically normal embryo. Any additional euploid embryos can be frozen and kept for the couple’s future use.
- Genetically abnormal embryos are discarded/destroyed
- This procedure may take a few weeks from commencement of the IVF cycle.
The newest method of analyzing these cells is by NGS (Next generation Sequencing) which analyses the genetic material at a very high resolution hence reducing the chances of erroneous reporting.
Embryo Biopsy on cleavage stage (day3)
Embryo Biopsy on blastocyst stage (Day 5/6)
What are the risks? Is the procedure Safe for my embryos & fetus?
This procedure requires the use of special equipment, training & skill. Improper embryo biopsy in unskilled hands can completely destroy the embryo.
Studies suggest that Preimplantation genetic testing & embryo biopsy does not harm the growth of the embryo or the fetus. The first baby through this procedure was born 1989 in London and since then this procedure has been used to deliver more than a thousand healthy babies worldwide.
While this procedure helps reduce the chances of conceiving a child with a genetic disorder; it cannot completely eliminate this risk. Further testing may be needed during pregnancy to reconfirm the genetic diagnosis.
We at Manipal Fertility have implemented the preimplantation genetic testing program in 2014 & with more than 100 patients treated with a success rate of 62%.
