Preimplantation genetic testing (PGT) for aneuploidies and embryo selection in ART

January 12, 2021

Preimplantation Genetic Diagnosis

Introduction

Infertility affects around 10-15 % of couples and the incidence is much higher in females with advanced age of more than 35 years ( >25%). Also the causes of infertility are different in a couple with advanced age of female partner as compared with a young couple. It is a well known fact that female infertility declines with age and chances of miscarriage are also increased in a women with advanced age. The most important reason for this is the embryonic defects which is mainly due to the defective oocyte quality. So to help these group of patients in achieving a successful pregnancy, we can offer them this newer technology of preimplantation genetic screening. This technique is also a boon for the couples with recurrent IVF failures and recurrent abortions.

Whom to offer – This technique can be offered to patients with following issues

1) Couples with advanced age of female partner (>35 years)

2) Couples with recurrent abortions.

3) Either of the partner is suffering from any single gene disorder or any chromosomal disorder.

4) Patients with recurrent ivf failures.

5) Couples with a previous child affected by any genetic disease.

Procedure Methodology

This procedure needs technical expertise and needs to be done by an embryologist who is skilled enough to carry out the procedure. The couple undergoes an ivf cycle and the resultant embryos are then subjected to biopsy. This can be done on either a day 3 embryo ( 8-cell stage), or a day 5 embryo ( blastocyst stage), however biopsy done at blastocyst stage is preferred. So the technique involves creating a small hole in the outer covering of an embryo ( also known as zona pellucida) with the help of non-contact laser, followed by a biopsy of 1-2 blastomeres from a day 3 embryo or 8 to 10 cells from the trophoectoderm layer of a day 5 embryo.

These cells then undergo genetic analysis either using a FISH technique ( 5 chromosomes including no 13,18,21 X and Y) or CGH array ( entire 23 pair of chromosomes are checked). Since it takes some 10 to 15 days for the results to come, so we need to freeze all embryos followed by the transfer of a genetically normal embryo in the next cycle.

1) Figure showing a day 3 biopsy

2) Figure showing a day 5 biopsy

Preimplantation Genetic Diagnosis

Advantages

This technique is definitely advantageous for those couples with advanced age because it has been observed that as many as 50 percent of grade 1 embryos might not be genetically normal, so when we select them according to their ploidy status, we can improve the ivf outcome and can give them a healthy pregnancy.

Also the patient can go for a single embryo transfer without compromising the success and hence we can reduce the burden of multiple pregnancy and the complications associated with it.

Conclusion

Preimplantation genetic testing is an upcoming technology which is very promising and it has improved the IVF outcome in patients with advanced age, recurrent miscarriages, recurrent ivf failures and patients with genetic disorders. So this technique should definitely be offered to these category of patients in order to improvise their success rate.

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