Preimplantation Genetic Testing (PGD & PGS)

What is Preimplantation genetic screening (PGS)?

Preimplantation genetic screening abbreviated as PGS refers to removing one or more cells from an in-vitro fertilization embryo to test for chromosomal normalcy. PGS screens the embryo for normal chromosome number. All of us humans have 23 pairs of chromosomes, totaling 46. Having an extra or a missing chromosome causes problems. An example of problems caused by chromosomal anomaly is Down Syndrome wherein the baby has an extra chromosome number 21. A PGS screening helps detect Down Syndrome and more such problems.

Why Preimplantation Genetic Screening (PGS)?

Several studies have shown that overall, about 50 per cent of human preimplantation embryos from IVF are chromosomally abnormal. The rate of abnormalities is affected greatly by female age. Chromosomes in eggs from older women have a significantly increased rate of abnormalities. To a great extent, chromosomal abnormalities are responsible for failure of implantation of IVF embryos. Chromosomal abnormalities are also responsible for about 70 percent of miscarriages in early pregnancy.

PGS is recommended when the doctor identifies you at increased risk for having embryos with abnormal chromosomes are best candidates for PGS. This may be the case when:

• Your maternal age is 35 or more
• You’ve had recurrent miscarriages
• Your previous IVF attempts have failed
• If you want only single embryo transfer
• You want to do family planning
• You desire to maximize the possibility of a healthy baby with IVF

Which abnormalities can be detected using PGS?

Specifically, PGS can identify chromosomal abnormalities such as:

1. Incorrect number of chromosomes or aneuploidy – Aneuploidy is the presence of an abnormal number of chromosomes in a cell, such as having 45 or 47 chromosomes when 46 is expected in a human cell.
   Examples of aneuploidy are:
   
   • Down Syndrome with an extra copy of chromosome 21,
   • Edwards Syndrome with an extra copy of chromosome 18
2. Translocation or rearrangement of one segment of chromosome onto another chromosome
3. Deletion or missing a segment of chromosome
4. Sex-chromosome abnormalities including duplication or deletion of X and Y chromosome
   Examples of sex-chromosome abnormalities include
   
   • Klinefelter Syndrome with three copies sex chromosome, two X and one Y
   • Turner Syndrome with only one copy of sex chromosome, one X

Benefits of Preimplantation Genetic Screening

By performing PGS, the doctor can ensure that the embryos selected for the transfer have a healthy number of chromosomes. This will help in preventing abnormalities that will impact the pregnancy. When an embryo has an abnormal number of chromosomes, it can prevent implantation, cause pregnancy loss, or create significant health problems in the baby, which can be very difficult on intended parents undergoing IVF.

• Improved embryo selection – PGS testing reduces the risk of miscarriage, decreases the time it takes to become pregnant, and lowers the need for transferring multiple embryos.
• Preventing genetic transmission of unknown abnormalities – PGS doesn’t test for specific diseases but looks for chromosomal abnormalities, such as the number and position. By performing PGS on your viable embryos, the doctor can select chromosomally normal embryos and rule out those that would prevent a healthy birth, even if they appear high-quality before screenings.
• Higher chance of a successful pregnancy – PGS gives the doctors insight into which embryos will be most likely to implant and develop healthily. If the embryos display specific abnormalities that prevent the transferred embryo from implanting within the uterus or developing during its early stages, the doctor can identify and abstain from transferring these embryos to optimize your IVF process.
• Quicker pregnancy – Using PGS, the fertility clinic can avoid unsuccessful embryo transfers by transferring the healthiest embryos first. By understanding which embryos will help in achieving a full-term pregnancy, you can ensure you’re not spending months transferring embryos that won’t lead to a successful pregnancy and birth.

Cost of Preimplantation genetic screening

A consent form is mandatory before a PGS screening is conducted. The average cost of a PGS in India is between INR 16,000 to INR 17,000.

A PGS screening is useful way to determine a successful pregnancy and spend less time undergoing multiple IVF cycles.