The greatest advance in the history of reproductive medicine has been the development and growth of human embryos resulting from in vitro fertilization. The embryos that are formed as a result of assisted production are then transferred into a woman’s womb, resulting in an anticipated pregnancy. These embryos can be tested for genetic abnormalities before they are transferred into the uterus.
There are 23 pairs of chromosomes in each cell in the human body. This includes all of the 20 trillion cells which we all have. Of these 23 sets of chromosomes, one pair consists of the sex chromosomes X and Y, which determine our gender, male or female.
For a couple of generations, we have been able to test whether a woman has a major chromosomal abnormality such as Down’s syndrome in her developing fetus and child. The procedures used to determine such devastating maladies are called amniocentesis and chorionic villus sampling. By definition, we call this prenatal testing.
The testing of human embryos is separate and distinct from prenatal testing because it is performed at the earliest stage of human development. In both cases human chromosomes are tested and evaluated to make sure they are correctly aligned and consist of the proper number of chromosomal pairs.
The testing for genetic abnormalities in embryos is referred to as preimplantation genetic screening. Formally it was designated as preimplantation genetic diagnosis. These embryos are called preimplantation embryos have not yet been transferred into a woman’s body. The important point to note is that testing these embryos is not primarily to determine the likelihood of an offspring born with the chromosomal conditions such as Down syndrome. The main reason we often utilize this type of genetic testing is to improve the likelihood of pregnancy and reduce the possibility of miscarriage, two remarkable medical feats.
We often think that the older woman is unable to conceive because she has fewer eggs, or eggs that are too old. The actual problem is a genetic one. The most common genetic abnormality that is seen is a chromosomal disorder. In most cases, it is due to an aberration in the number of chromosomes. Most commonly, a reduction of the number of chromosomes will be seen, particularly with respect to the sex chromosomes. In some cases, the number of chromosomes can be abnormally increased.
The results of genetic testing has confirmed that the main cause of the failure of an embryo to implant is because of an imbalance in the number of chromosomes or the alignment of chromosomal material. When genetic testing shows that there are no chromosomal abnormalities, then the likelihood of implantation is markedly increased, and the likelihood of miscarriage is markedly reduced.
The basic method for genetic testing of embryos is called FISH, which stands for fluorescent in situ hybridization. This procedure only screens 8 to 12 pairs of chromosomes. It tests for the most common chromosomal disorders but it doesn’t test all of the remaining chromosomes. A fresher technology called comparative genomic hybridization allows for the testing of all 23 pairs of chromosomes. The use of these new remarkable genetic tests can help a couple achieve the dream of a healthy, happy baby.
To learn more about fertility treatments, contact Dr. Brody.