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Preimplantation Genetics PGS/PGD

IVF Genetics

Evidence-Based Fertility Services in San Diego

The most common reason for embryos to fail implantation or to produce a healthy pregnancy is that they have an abnormal number of chromosomes. As many as 30 percent of fertilized human eggs have such abnormalities. We hope to improve the success rate of IVF by selecting embryos with the normal number of chromosomes to transfer into the uterus.

Traditionally in IVF procedures, doctors and embryologists visually inspect embryos and then decide to transfer those that appear morphologically healthy after 5-6 days of development. Many IVF centers transfer more than one embryo at a time, because many of them won’t result in a successful pregnancy. However, if multiple embryos do implant successfully it can be risky for both the mother and the fetus.

To reduce such risks, we only transfer a single embryo at a time, and new genetic screening technologies are helping us ensure that we select the most viable and healthy one.

PGS with aCGH

Preimplantation Genetic Screening with aCGH (array Comparative Genetic Hybridization) technology. Array-CGH is used extensively worldwide, and it was the first technology to be widely available for analysis of chromosomal abnormalities in the embryo. This screening is also called aneuploidy testing: counting the number of chromosomes present in a cell.

Aneuploids are cells that do not have exactly 46 chromosomes. Embryos with a healthy set of chromosomes are called euploid. aCGH testing of embryos allows us to determine the number of chromosomes in each embryo before they are transferred into the mother’s uterus.

aCGH chromosome screening offers much more precise information than standard genetic testing has in the past. During CGH testing all chromosomes including X and Y are analyzed and compared to a sample of “normal” DNA. The advantage of doing aCGH testing over traditional testing is that all 23 pairs of chromosomes can be tested, which leads to more accurate results that aneuploidy.

PGS with NGS

The next generation DNA sequencing technique is a high throughput method, meaning it allows researchers to quickly conduct millions of genetic tests in a short time frame. With its scalability and speed, next-generation sequencing enables researchers to study biological systems at a level never before possible.

The next generation DNA sequencing technique for screening embryos has proven to be an effective and reliable method of selecting the best embryo to transfer to in-vitro fertilization patients. Because the technique is less expensive, faster, and, most importantly, accurate, researchers believe it has the potential to revolutionize pre-implantation genetic screening.

DNA sequencing also enables us to explore other potential causes of IVF failure beyond changes in chromosome numbers. Genetic testing companies are testing whether an embryo’s particular mitochondrial genome, the discrete genetic sequence found in the energy-producing structures of cells, has an effect on the procedure’s success.

PGD

Preimplantation genetic diagnosis (PGD) is a screening test used to determine if genetic or chromosomal disorders are present in embryos produced through in vitro fertilization (IVF). PGD tests embryos before they are transferred to the uterus, so patients can make informed decisions selecting embryos unaffected by the genetic or chromosomal disorder for transfer.

Preimplantation genetic diagnosis may be recommended to patients when:

  • One or both partners has a history of heritable genetic disorders
  • One or both partners is a carrier of a chromosomal abnormality
  • The mother is of advanced maternal age
  • The mother has a history of recurrent miscarriages

PGD can be used to determine if embryos produced through in-vitro fertilization carry a gene mutation associated with a specific genetic disorder, such as cystic fibrosis or muscular dystrophy. PGD is also offered to couples when one partner has a chromosomal abnormality, such as an unbalanced translocation. If the abnormality is present in the embryo, the condition could ultimately prevent embryo implantation, lead to pregnancy loss, or result in the birth of a child with congenital malformations or mental retardation.

Genetic Carrier Screening

There are several genetic conditions that are more common in specific ethnic groups. The information below briefly reviews some general information about testing for these conditions. If you have questions about this information, please address them with the doctor during your scheduled appointment.

What are genes?

Genes are made up of DNA and are the codes or instructions that tell the body how to grow and develop. These genes are arranged on strings of information called chromosomes. We have two copies of each chromosome, one that is inherited from our mother and one that is inherited from our father; as a result, we have one copy of each gene.

What are recessive diseases?

Many conditions are now known to be caused by changes, or mutations, in genes. Some genetic conditions, known as recessive conditions, are caused when a change or mutation is present on both genes of a pair. This means that both the mother and father must pass on the same changed gene in order for a child to have a recessive condition.

What is a carrier?

A carrier is a person who has a change in only one gene of a pair and the other gene of the pair is working normally. A carrier is sometimes said to have the disease trait but has no physical symptoms of the disease. In many families, a recessive gene change or trait can be passed on through generations without ever being known. A recessive disease can only occur if a person who is a carrier has a baby with another person who is also a carrier. Such a couple would have a 1 in 4 (25 percent) chance, in each pregnancy, of having a baby with that recessive disease.

Who should be screened?

DNA tests are available to help a couple determine if they are carriers of the same recessive disease trait and are at risk for having children with that recessive condition. Some diseases occur more often in certain ethnic groups. Information about the carrier frequency of the more common recessive disease traits in certain ethnic groups is provided below. There are many other recessive conditions, not listed below, for which testing is not typically performed because the conditions are less common or because testing is not available.

ETHNICITY
DISEASE
CARRIER FREQUENCY

Ashkenazi Jewish:
Tay-Sachs
1/30
Canavan
1/40
Cystic fibrosis
1/29
Familial Dysautonomia
1/30
Mediterranean:
Cystic fibrosis
1/20-1/50
Sickle cell anemia
1/30-1/50
European Caucasian:
Cystic fibrosis
1/29
African American:
Sickle cell anemia
1/10
Thalassemia
1/30-1/75
Cystic fibrosis
1/65
Asian:
Thalassemia
1/20-1/50
Cystic fibrosis
1/90
Hispanic:
Cystic fibrosis
1/46
French Canadian:
Tay-Sachs
1/15
Cystic fibrosis
1/29
How can I have carrier testing?

If you are interested in learning more about the genetic conditions more common in your specific ethnic group and the availability of carrier testing for these conditions, please ask our physician. You may also wish to check with your insurance company about whether this testing would be covered under your plan.

Hanabusa IVF is collaborating with Good Start Genetics to perform genetic carrier screening. Please visit their website to learn even more about this topic.

https://www.goodstartgenetics.com/our-tests/genevu-carrier-screening/

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