Understanding what the research tells us about PGT-A and embryo selection

Scott et al. | Fertility and Sterility | June 2013

When undergoing IVF, patients often wonder whether genetic testing can improve their chances of pregnancy.

One commonly discussed technique is preimplantation genetic testing for aneuploidy (PGT-A), which screens

embryos for chromosomal abnormalities before transfer.

But does testing actually improve IVF success, or does it primarily help identify which embryo to transfer first? A

randomized controlled trial published by Scott and colleagues in 2013 offers some insight.

What did the researchers investigate?

The study included 155 patients and compared two approaches to embryo selection:

• Chromosome screening: Embryos were assessed based on their appearance and underwent

comprehensive chromosome screening (CCS), an earlier form of PGT-A, using a biopsy of cells from the

blastocyst’s outer layer.

• Morphology-based selection: Embryos were selected based on their appearance under the microscope,

without chromosome screening.

The researchers then evaluated implantation and delivery outcomes.

What were the findings?

The study reported higher success rates in the group that underwent chromosome screening.

Outcome With screening Without screening

Implantation resulting in delivery per

embryo transferred

66.4% 47.9%

Patients achieving a delivery following

fresh embryo transfer

84.7% 67.5%

These findings suggest that chromosome screening may help clinicians select embryos with a higher likelihood

of successful implantation and delivery. However, the results need to be interpreted in the context of the study

population and its design.

Do these results apply to every IVF patient?

Not necessarily. The participants had relatively favorable prognostic characteristics, including good ovarian

reserve indicators, and had at least two blastocysts available before randomization.

PGT-A does not create additional embryos. Its usefulness depends, in part, on how many embryos a patient

produces and how many are suitable for testing and transfer. For patients who produce only one or two

embryos, testing may provide useful information, but it may not increase the likelihood of having a baby. There

may also be no additional embryo available for selection if testing identifies none as suitable for transfer.

Transfer timing also differed between the groups: embryos in the screening group were transferred on day 6,

while those in the control group were transferred on day 5. Therefore, the results cannot be attributed to

chromosome screening alone with complete certainty.How does PGT-A help in practice?

PGT-A screens embryos for abnormalities in chromosome number. It can help identify embryos classified as

euploid, meaning they have the expected number of chromosomes, and distinguish them from embryos

classified as aneuploid.

Consider a patient who has four blastocysts available for transfer. Without PGT-A, the embryology team selects

an embryo based primarily on its morphology, or appearance. If the first embryo does not result in a live birth,

another embryo may be transferred in a subsequent cycle.

With PGT-A, chromosome results provide additional information to help prioritize embryos for transfer. This may

improve the chance of success per transfer or reduce the number of unsuccessful transfers in some patients.

However, identifying an embryo with a normal chromosome result does not make that embryo

genetically healthier than it was before testing, nor does testing repair chromosomal abnormalities. It

provides information that can guide embryo selection.

Does PGT-A increase the overall chance of having a baby?

Improving the chance of success per embryo transfer is not necessarily the same as increasing the cumulative

live birth rate—the chance of having a baby after using all embryos from a single egg retrieval.

A patient may achieve a successful pregnancy sooner with PGT-A because an embryo with a higher likelihood

of success is selected first. However, without testing, that same patient might eventually achieve a live birth after

transferring another embryo.

The 2013 trial demonstrated improved outcomes under its specific study conditions, but it did not establish that

PGT-A increases cumulative live birth rates for every patient undergoing IVF. Potential benefits depend on

factors including maternal age, embryo number, reproductive history, and the individual clinical circumstances.

The takeaway

The study by Scott and colleagues supports the potential value of chromosome screening for embryo selection

in patients with characteristics similar to those studied. However, PGT-A is not necessary for every IVF patient,

and its benefits should be considered individually.

A euploid PGT-A result does not guarantee implantation, pregnancy, or live birth. PGT-A is a screening test for

chromosome-number abnormalities, not a comprehensive test for every genetic disease.

The key question is not simply whether PGT-A can improve embryo selection, but whether it is likely to

improve outcomes for a particular patient.