Through ovarian stimulation, we aim to produce many eggs, which will hopefully grow into a small group of embryos.

But when there are many embryos to choose from, how do we know which ones are the best?

There are several ways to pick an embryo.

Traditionally, the embryologist uses morphology, the size and appearance of the embryo, to determine which embryos are suitable for transfer and freezing.

Using morphology for embryo selection is not harmful to the embryo and carries no additional cost.

However, morphology is subjective.

An embryo with a lower grade may still result in pregnancy, and a high grade embryo may not.

Another way to select between embryos is through pre-implantation genetic testing.

In order to make a typical baby, an embryo must be created from an equal amount of genetic material contributed by the sperm and the egg.

We are all made up of a unique set of DNA, which we inherit from our genetic parents.

DNA is organized into genes, and genes are packaged into larger structures called chromosomes.

If you think of each person as a library, the chromosomes are the books that make up the library, genes are the sentences within the books, and DNA is the individual letters.

Each of us typically has 46 chromosomes arranged into 23 pairs, termed euploid.

We all have two copies of every chromosome, one copy from the egg, and one from the sperm.

The first 22 pairs of chromosomes are numbered 1 through 22 based on size.

The 23rd pair are sex chromosomes, XX for female or XY for male.

Genetic diseases can result from errors in part of a chromosome or the entire chromosome.

The most common cause of miscarriages and IVF failure is an embryo having too many or too few chromosomes.

This is called aneuploid.

Although this problem can arise from either the sperm or the egg, it is more common in eggs from women over 35 to 40 years old.

IVF can help this problem by creating more eggs, increasing the pool of embryos we have to choose from.

Then if we can identify the embryos that contain too many or too few chromosomes, we would avoid selecting those embryos.

This is pre-implantation genetic testing for aneuploidy, or PGTA.

PGTA is the modern terminology, but in the past has also been referred to as PGS or TCS.

Here's how it works.

All good quality embryos that make it to the blastocyst stage by day 5 or 6 are biopsied.

A few cells are removed from the trophectoderm, or placenta, of each embryo.

Embryo damage is very rare.

The embryo is then frozen and stored in our labs.

The biopsy cells are sent to a genetics facility that analyzes the DNA to determine if the embryo contains the normal 46 chromosomes.

This allows for the transfer of a chromosomally normal embryo, which will have a potentially higher chance of implantation than an untested embryo where we don't know the chromosomal makeup.

It's important to note that PGTA increases cost by $4,000 or more, and there's a small chance that the genetic tests may return with no result.

PGTA is a useful test, but even a chromosomally normal embryo does not guarantee pregnancy, nor does it completely prevent miscarriage.

Pregnancy rates for PGTA-tested euploid embryos are upwards of 60 to 70%.

You will need to undergo a frozen embryo transfer cycle to transfer the normal embryo into the uterus.

PGTA is most beneficial for women who are over 37 to 38 years old and have multiple embryos.

Once pregnant, prenatal genetic screening is still recommended because, although it's very accurate, there is a chance that PGTA can be incorrect.

Even though PGTA does not create better quality embryos, it can provide valuable information and help to identify the euploid embryo sooner.

At PCRM, we perform a high number of PGTA cycles, and our genetic counselors would be happy to meet with you and answer your questions.