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Genetic Tests

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Does anyone know what the RE looks for when they do a genetic screen on the embryos? How it's done and what exactly do they screen for? Is it a common practice?

 

Thanks, Rebecca

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Hey!

 

My IPS had PDG done and here is the write up and info they have on our clinic's website

 

PGD

 

Preimplantation Genetic Diagnosis (PGD) is a relatively new procedure in which eggs or embryos are tested for certain genetic conditions prior to being replaced in the womb.

 

Children born in the United States have a 3% to 4% chance of a major birth defect. Some of these abnormalities occur because of a problem with a single gene which is inherited from one or both of the parents, while other abnormalities are related to an abnormal number of chromosomes (aneuploidy). Both of these problems can be diagnosed before embryos are transferred to the uterus and this diagnostic procedure is called preimplantation genetic diagnosis (PGD).

 

The majority of PGD procedures are performed for aneuploidy or abnormalities in the number of chromosomes and this problem increases with increasing maternal age. Studies have also shown that up to 85% of aneuploids are caused by the egg while the sperm may cause the remainder.

 

With respect to single gene defects, these defects can be dominant and are transmitted by one parent alone with a risk of an affected child being 50% (e.g. Myotonic Dystrophy) or these defects can be recessive and both parents must have the gene with a risk of an affected child being 25% (e.g. Cystic Fibrosis, Sickle Cell Anemia or Tay-Sachs Disease). There are now more than 50 single gene diseases that can be diagnosed with PGD. Most of these genetic syndromes are relatively uncommon.

 

Preimplantation Genetic Diagnosis is an intricate procedure, which involves removing a single cell from a three-day-old embryo and testing it for chromosomal disorders. PGD permits the selection of embryos, which are less likely to have chromosomal abnormalities and also embryos that may be free of a known single gene disorder, thereby increasing the likelihood of a healthy baby and decreasing the chances of having to terminate a pregnancy found to be abnormal through chorionic villus sampling or amniocentesis.

 

Even in optimal situations, like egg providers under age 30, the percentage of embryos that have normal chromosomes may only be approximately 50%. This may explain the frustration that patients and IVF specialists feel when apparently normal looking embryos are transferred with negative results or recurrent losses, sometimes even after multiple IVF attempts. Chromosomal abnormalities in embryos are therefore responsible for a significant proportion of failed implantations after hormonal, uterine and immunological factors have been excluded.

 

Couples can benefit from PGD when the woman is 35 or older, by testing for age-related chromosomal disorders, also called aneuploidy, or when there is a single gene defect within a family. Younger women with repeated unexplained miscarriages can also benefit from this test. The purpose is to select and replace only those embryos that appear to be normal so that women may increase the chance of conceiving while reducing the probability of losing the pregnancy or carrying an abnormal baby to term. PGD for aneuploidy can determine the presence or absence of a certain number of chromosomal disorders, but cannot detect genetic disease nor predict congenital malformation.

 

 

 

PGD for aneuploidy

Females are born with all the eggs they will have in their lifetime. As a woman advances in age, her eggs are exposed to aging processes that include chromosomal abnormalities. Thus, the chance of conceiving a chromosomally abnormal baby increases with age. In complete contrast, sperm in the male are newly made every 65-75 days. Chromosomes are string-like structures found in the center of the cell, the nucleus. Chromosomes contain genes that are made of DNA, the molecule that contains inherited information. Normal human cells contain 23 pairs of chromosomes, a total of 46. We receive 23 chromosomes from each parent. If an error occurs leading to the egg or sperm having an extra or missing chromosome, the embryo created by that egg or sperm would have an extra or missing chromosome. This situation is called aneuploidy. If the aneuploidy involves chromosomes such as 13, 18, 21, X or Y, the pregnancy may still carry on until birth, even though the fetus has a chromosomal disorder. This produces an effect called Down’s syndrome. The effects of other common aneuploidies include Turner’s syndrome and Klinefelter’s syndrome. These disorders are non-fatal, in that the fetus can carry to term and result in a live birth, although the baby is abnormal. Overall, the risk of aneuploidy is known to increase with maternal age, from 1/385 at 30, 1/179 at 35, 1/63 at 40 and at the age of 45 the chance of delivering an affected child is 1/19.

 

Advantages

PGD for aneuploidy provides three advantages for conception and child bearing. The first is to improve the chances of pregnancy. Even though only about 9 out of 23 chromosomes can be tested, these 9 are the ones that most commonly cause problems. By replacing only embryos believed to be chromosomally normal, there is an increase in implantation for those patients at risk, as shown in two recent studies. The second advantage is a reduction in pregnancy loss. For women of 35 and over, as much as 35% of pregnancies are miscarried; in up to 50% of these cases, the chromosomal abnormality of aneuploidy is the cause. These figures are approximately the same whether the pregnancy is after an IVF procedure or in the general population. Again, recent studies have shown a possible reduction in pregnancy loss by half after PGD for aneuploidy. Thirdly, and most importantly, is the increased chance of giving birth to a chromosomally normal baby. So far (July 2002), in 357 live births and ongoing conceptions obtained after PGD at the Institute for Reproductive Medicine and Science of Saint Barnabas, two pregnancies spontaneously aborted (0.56%), which were chromosomally abnormal, a 4.8 fold reduction for that group of patients according to their maternal ages - a considerable decrease.

 

Benefits

More than 20% of embryos from women aged 35 to 39 are generally affected; over 40, almost 40% of embryos are affected. These high numbers are not reflected in live births because most of the affected embryos will fail to attach to the womb; and those that do, will miscarry earlier or later during the pregnancy. Any embryo with a missing chromosome (monosomy) will cease to grow before implantation (except monosomy X and 21), and only a few of those carrying an extra chromosome (trisomy) will go to term. These are believed to be the main reasons why pregnancy and birth rates in women of 40 and over are so low. We have seen the most beneficial effect of PGD of aneuploidy in women 38 and older. However, PGD for aneuploidy is not only recommended for women 38 and older but also for younger patients with a history of previous trisomic conceptions, miscarriages, or repeated IVF failure. The purpose of PGD is therefore to select for replacement only those embryos believed to be chromosomally normal; aiming to achieve higher implantation per embryo replaced, a reduction in pregnancy loss, and a higher proportion of healthy offspring.

 

Procedure

The preferred method of PGD is to remove one cell from an embryo (blastomere) on Day 3 of development; at this stage the embryo usually has 6 to 10 developing identical cells, each with a full complement of chromosomal material. The embryo(s) remain in incubation while the cell is analyzed. PGD is accomplished by making a small opening in the embryo(s) outer shell (zona pellucida) and the blastomere is extracted with a micropipette. The Day 3 embryo is exposed to an elevated level of sucrose in order to reduce the size of their cells. This is to simplify the removal of cell(s), because connections between them can be very firm. The process also requires the temporary removal of calcium and magnesium from the culture medium. Normally, only a single cell is removed from each embryo as it is expected to be identical to all the other cells, but it may be necessary to remove a second cell according to circumstances. In either of the above cases, the analysis of the biopsied cell(s) uses a technique called fluorescence in-situ hybridization or FISH, which takes about one day. The cells are glued to a glass slide and heated and cooled and their DNA is 'labeled' with colored fluorescent dyes called probes, one for each chromosome analyzed. At present, the test can check about 9 chromosomes out of 23. Once the FISH procedure is complete, the geneticist counts the colors using a powerful microscope, thereby distinguishing normal and abnormal cells. This information is then related to the normalcy of the associated embryo being held in culture. After this process the biopsied and analyzed cells are no longer viable in any way, and the slides on which they sit are placed in a deep freeze for future reference.

 

Implantation Rates

If one looks at the implantation rate of embryos that test normal on PGD; it appears as though each normal embryo in patients over 40 carries a 15% chance of making a baby. PGD in patients where the egg provider is 35 to 39 years yields a 25% chance, while egg providers under 35 years yield at 38% chance of a baby with one embryo that tests normal. From this, we can see that we still need to be aggressive when transferring embryos after age 40.

 

In addition, the proportion of embryos that test genetically normal with PGD appears to be around 45% under age 35 and this percentage drops to somewhere between zero and 20% after age 40. There are individual instances where patients, at all ages, may have either no normal embryos or more than the expected percentage for their age. Single Gene Disorders Close

Cystic fibrosis

Tay-Sachs disease

Sickle cell anemia

Hemophilia

a-thalassaemia

B-thalassaemia

Fanconi anemia

Gaucher disease

Phenylketonuria

Fragile X syndrome

Duchenne muscular dystrophy

Myotonic dystrop

Von Hippel-Lindau disease

Incontinentia Pigmenti

Marfan Syndrome

Medium chain acyl-CoA

Dehydrogenase deficiency (MCAD)

Osteogenesis imperfecta

Retinitis pigmentosa

Spinal muscular atrophy

Lesch-Nyhan syndrome

Breast cancer (BRCA1/BRCA2)

 

If you have a genetic disorder not represented in the list above, please contact us. New tests for genetic diseases are emerging regularly and may be available.

 

(this was copied from the site www.goivf.com)

 

 

A lot of info hope some of it helps.

 

This cost my IPS extra but I think it is worth the money as ou for 21 eggs(cannot recall if there were more) only 7 tested normal.

 

Good Luck!

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This is such great info that I am moving and pinning it in the Cycling and 2ww section.

 

Thank you for the info. I know that this has been asked more than once!!

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My genetic disorder, Neurofibromatosis, is not listed there, but there is a PGD test available.

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