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What Is Preimplantation Genetic Testing (PGT) & How Does It Increase IVF Success?

  • Category: Education
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  • Written By: Kathryn C. Calhoun, MD, ACRM
What Is Preimplantation Genetic Testing (PGT) & How Does It Increase IVF Success?

The Atlanta Center for Reproductive Medicine (ACRM), a Colorado Center for Reproductive Medicine (CCRM) Network Clinic, offers preimplantation genetic testing (PGT) to identify the embryos that are most likely to result in a live birth.

We offer three types of PGT:

  • PGT-aneuploidy (PGT-a), also known as Comprehensive Chromosome Screening or CCS, for chromosomal abnormalities
  • PGT-structural rearrangement (PGT-SR), which screens for chromosomal rearrangements caused by structural rearrangements within the parental chromosomes.
  • PGT-monogenic disorder (PGT-m) which tests for specific gene mutations.

By utilizing the latest assisted reproductive technologies, ACRM’s comprehensive genetic services optimize fertility care, so patients may achieve their ultimate goal, a healthy baby.

Chromosomes, Genes & DNA

Humans have a total of 46 chromosomes, 23 are inherited from each parent. Forty-four of these are called autosomes and are present in both sexes. The final pair is called the sex chromosomes (X and Y). Each chromosome contains hundreds to thousands of genes, which are short sections of DNA that code for proteins that govern the features and functions of our body.


The CCRM Network uses a proprietary PGT-a technology called Comprehensive Chromosome Screening (“CCS”) to identify embryos that have the correct number of chromosomes. These embryos are called “euploid” embryos and are more likely to result in a healthy, live birth.

If an embryo has too few or too many chromosomes, it is usually not able to survive. These embryos are called “aneuploid” embryos. Exceptions do exist, including Down's syndrome (Trisomy 21, which is three copies of the 21st chromosome). Other exceptions are Trisomy 13 and 18 (3 copies of chromosome 13 and 18 respectively) where, despite being live born, these offspring rarely survive more than a few months due to severe birth defects. Some cases of too many or too few sex chromosomes, such as Turner's Syndrome (45 chromosomes - only one X) and Klinefelter's Syndrome (47 total chromosomes-two X’s and one Y), are able to survive but may have a wide spectrum of health problems.


If a patient has a structural rearrangements within their own chromosomes (i.e. translocation, inversion), they are more likely to have embryos with chromosomal abnormalities. Sometimes, these rearrangements cannot be detected by CCS/PGT-a alone, and we must employ additional testing to identify the healthiest embryos. PGT structural rearrangement (PGT-SR) screens for chromosomal rearrangements caused by parental structural rearrangements.

What is the difference between CCS/PGT-a and PGT-m?

CCS/PGT-a allows us to assess the chromosomes of an embryo and therefore serves as a screening tool for finding embryos that are more likely to result in a live birth.

PGT-m allows us to see if an embryo has a specific gene for a disease (i.e. Cystic Fibrosis, Muscular Dystrophy, BRCA.) These genes do not cause infertility or miscarriage, but they could increase the chances of the baby being born with a life-altering and/or life-threatening condition. PGT-m is useful when one or both parents (or their family members) carry a gene mutation and we know exactly what disease we are diagnosing.

Who Should Consider CCS/PGT-a ?

All patients are at risk of having embryos with chromosomal problems and this risk increases with age, primarily female (egg) age. A woman who is under the age of 35 can expect about 20-30% of her embryos to be abnormal, a 38 yr old woman can expect 50% of her embryos to be abnormal, and a woman in her 40s can have > 75-80% abnormal embryos. Patients with recurrent miscarriage or unexplained infertility may have higher percentages than other patients their age.

CCS/PGT-a improves the chance of live birth for all couples but would be expected to make the greatest improvements for women > 35 years old, patients with multiple unexplained miscarriages and patients who are not responding to routine fertility treatment and have had repeated failure.

How Does CCS/PGT-a Increase IVF Success?

CCS/PGT-a identifies embryos that have the highest chance of making a healthy baby, thus reducing the number of embryo transfers to find the “right embryo” and increasing the efficiency and success of in vitro fertilization (IVF).

Further, we can transfer just one embryo at a time and still enjoy a high chance of success, thereby eliminating the risks of a multiple pregnancy.

IVF with CCS Success Rates

IVF by itself is already an extraordinarily powerful tool in reproductive medicine. Whereas the normal human fecundity rate (likelihood of pregnancy per cycle) is ~20%, IVF fecundity rates are almost twice as high as that (when we average all ages together). IVF with CCS rates are higher yet, surpassing 60%, because we can further fine-tune the process of identifying which embryos to consider for transfer into the uterus.

For more information about CCS, or to schedule a New Patient Appointment please contact ACRM by calling 678.841.1089, or click here.