Every expectant parent wonders if their babies are normal and healthy. The truth is that all women have a risk of a pregnancy with abnormal chromosomes, particularly if the woman is above 35 years old.

In the past, pregnant women above 35 may be tested with chorionic villus sampling (CVS) or amniocentesis for chromosome abnormalities, such as Down Syndrome. However, they will have to make the painful decision to either keep or stop the pregnancy when the babies are found to be abnormal.

Pre-implantation genetic diagnosis (PGD), also known as Pre-implantation Genetic Screening (PGS) eliminates the dilemma of deciding on pregnancy termination in the event the tested fetus turns out to be abnormal, as only chromosomally normal embryos are replaced into the womb. PGD is highly recommended for women above 35, patients with inherent genetic diseases, recurrent miscarriages and IVF failures, or sexually-related diseases.

PGD is done in conjunction with an IVF cycle. With PGD, one or two cells are taken from the embryo on Day 3 or 5, and assessed for chromosomal defects that may lead to miscarriages or genetic disorders. This technique ensures only embryos that are healthy will be selected for transfer into the uterus for implantation, improving the likelihood of a successful pregnancy and the birth of a normal baby.

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There are different types of PGDs for different functions

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PGD – FISH

Fluorescent In-Situ Hybridization (FISH) is the first technique used to detect numerical chromosomal abnormalities such as Down’s Syndrome, Patau Syndrome or Edward’s Syndrome. It can also be used to detect abnormalities in the sex chromosomes (X & Y) such as Turner’s Syndrome, Klinefelter’s Syndrome and Super Female XXX. Newer tests are now available as this test has its limitations.

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PGD – PCR

A technique known as Polymerase Chain Reaction (PCR) is usually performed to detect genetic disorders such as Alpha-thalassaemia, Beta-thalassaemia or Haemophilia. The PCR technique involves a highly sensitive analysis of the embryo’s DNA to check for abnormalities.

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PGD – Micro-array CGH (24-Chromosome Aneuploidy Screening)

This screening is usually recommended for women, usually above 35 of age, with recurrent miscarriages. Most fertilty centres are only able to screen 5-12 chromosomes. TMC Fertility Centre is the first centre in Asia to offer the Microarray CGH (aCGH) PGD, which enables us to screen all 24 chromosomes (including the sex chromosomes) at the same time.

This helps to confirm that the embryo has the correct number of chromosomes before transferring to the uterus, leading to a successful pregnancy and increasing the likelihood for a couple to have a normal and healthy baby. This is particularly helpful in women in higher age groups, as abnormal embryos increase with the patients’ age. The success rates of a 40 year-old woman, is almost similar to a 28 year old-woman if chromosomally normal embryos are replaced after PGD testing.

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PGD-NGS

The Next Generation Sequencing (NGS) PGD is the most advanced pre-implantation screening to date, with each sample given an additional molecular code to eliminate the possibility of errors. The DNA collected from the embryo is tested directly, without the use of lights or markers as with earlier PGD screenings.

The PGD-NGS tests all 24 chromosomes with a single cell from the embryo, and contains information that indicates not just the condition of the embryo but the potential health risks of the child decades down the line. NGS is expected to change the world of genetics in time to come, offering uncannily accurate predictions of a person’s health conditions even before birth, fully embodying its name as a screening of the ‘next generation’.