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:
- 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
- Translocation or rearrangement of one segment of chromosome onto another chromosome
- Deletion or missing a segment of chromosome
- 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
