Genetic Screening

Preimplantation Genetic Screening?

Preimplantation Genetic Screening is a test that carefully examines the chromosomal material of an IVF or in-vitro fertilized egg before the process of implantation can begin. During this time, one or more cells are removed from the embryo to test it for numerical chromosomal abnormalities, also known as aneuploidy.

In this method, the screening allows for selective implantation of embryos once the healthcare professionals are aware of which ones have a standard number of chromosomes.

PGS is not recommended or required for everyone. Women over 37 have a higher chance of carrying eggs with an incorrect number of chromosomes. Thus, the screening process becomes necessary for them if they wish to conceive. Studies suggest that abnormal chromosomes are among the leading reasons women of that age have trouble conceiving. They are also more likely to have a miscarriage or a baby with Down’s Syndrome.

There are other situations when your doctor might recommend PGS. These include –

1) If your family has a history of chromosomal problems
2) If your sperm has a risk of carrying an abnormal number of chromosomes
3) If you have already had some failed miscarriages
4) If you have had failed IVF tries without any explanation

That said, PGS is not a guaranteed way to prevent a miscarriage or have a baby. Moreover, the studies about the screening process helping the groups mentioned above are limited.

You need the test for a variety of reasons since it can be used in different circumstances. They include –

1) Testing for monogenic disease –

In this case, the specific gene mutation carried by both parents is analyzed. After all, a disorder in a particular gene is due to a mutation in the DNA sequence. It results in diseases like cystic fibrosis or sickle cell anemia. There can also be inherited genetic mutations that might eventually develop into breast or ovarian cancer.

Some of the most common diseases tested via this method include –

• Huntington’s disease
• Sickle Cell Anemia
• Cystic fibrosis
• Muscular dystrophy
• Fragile-X syndrome
• BRCA1 and BRCA2 mutations
• Tay-Sachs disease

2) Testing for chromosome structural arrangement –

It analyzes embryos of parents who have chromosomal structural rearrangements like inversion or translocation. If unaddressed, it could result in miscarriages. The most common disorders examined through this process include –

• Reciprocal translocations
• Non-reciprocal translocations
• Robertsonian translocations

Thus, depending on your underlying condition, the PGS process will help you realize possible complications that might arise during childbirth.

In PGS, the biopsy is usually taken at the blastocyst stage, during the fifth or sixth day of embryo development. The embryos are frozen at the clinic, while the biopsies take place in the lab. PGS screens every embryo biopsy and then quantifies the number of chromosomes in each sample.

The result can either show an average number of chromosomes, which means that a chance of healthy pregnancy is relatively high, or it can show an abnormal number of chromosomes, meaning that there might be a miscarriage or other complications.

After the embryos are analyzed, a genetic report is sent to the medical professional. Based on this, along with the embryos’ grading and morphology, the doctor recommends which ones should be used for couples trying to get pregnant.

While PGS is a typical process, there are some risks attached, which is the case with all medical procedures. They include –

1) Ovarian hyperstimulation syndrome, which results in multiple pregnancies and might even lead to congenital disabilities unrelated to the genetic test.

2) The risk of biopsies or freezing harming the embryo.

The main indications for the need for PGS rise when the couples have single-gene disorders or structural aberrations in the chromosomes. On the other hand, there aren’t any fixed conditions for PGS, but it is mostly undertaken by women above 35 or if they’ve had failed IVF processes and miscarriages.

PGD or Preimplantation Genetic Diagnosis provides information about the gene make-up of the cells found in the embryo. In the embryo biopsy, 3-8 cells are removed from the source on day five and then sent to the lab for testing.

During this time, the embryo is frozen so that it can be implanted later. PGD can identify nearly 2000 inherited single-cell disorders and accurately identify affected and unaffected sources, up to 98%.

PGT is interchangeably used for PGS nowadays, but one must remember the screening process doesn’t take place in a vacuum. It is part of the IVF procedure, and thus the cost is relatively high. The average price is nearly $4,000. It includes consultations, lab fees, medications, additional investigations, and follow-ups.

Before considering PGT, you have to see if the pros outweigh the cons, especially since it is a pretty expensive process overall. The advantages of PGT are –

1) Reduced risk of having a child with a chromosomal abnormality.

2) Women with previously unexplained miscarriages might undertake PGT to prevent the situation from happening in the future.

3) It helps settle the difficult decision of whether to continue or terminate the pregnancy if the fetus has an abnormal chromosomal count.

4) For women above 36, the process reduces the risks of miscarriage and the number of transferred embryos required for pregnancy.

The downsides of PGT are –

1) It doesn’t increase the chances of having a baby
2) The cost is quite expensive

Some of the alternative methods which are likely to work better include –

1) Chronic villus sampling – CVS is a biopsy of the placenta 10-12 weeks into the pregnancy. If any anomaly is detected, the couple can consider termination.

2) Amniocentesis – The process is carried out 16-18 weeks into the pregnancy, and the amniotic fluid is tested for anomalies. Again, termination is an option.

3) Ultrasound and Blood Tests – While these two combined might work, the above processes have a greater accuracy rate.

4) In case of a high risk of inherited diseases, one might consider donor eggs or sperms.

Thus PGS is an additional test that might be carried out. That said, if couples want to undergo the procedure, they should consult the medical professionals beforehand.