IVF and PGD

PGD, Preimplantation Genetic Diagnosis- Genetic Disease Screening and Family Balancing

PGD, was made possible by advances in In vitro fertilization (IVF) which revolutionized infertility treatment and opened the door for many new and exciting technologies. These technologies include intracytoplasmic sperm injection (ICSI), which gave “infertile males” new hope for creating genetically related children.

PGD for Gender Selection, Family Balancing

PGD is offered by our Salt Lake City, Utah infertility clinic and it provides a means to screen embryos for specific abnormalities prior to uterine transfer in an IVF cycle. PGD can screen for an abnormal number of chromosomes (aneuploidy), chromosomes that are broken or translocated, and specific genetic diseases.

PGD Preventing Genetic Disease

PGD allows for preventing the transmission of sex linked genetic diseases. These are disorders that can only be present in a child of a particular sex. For example, hemophilia A and B are X (female chromosome) linked recessive and can only occur in males (XY). If a woman has the gene for hemophilia, after PGD only female embryos will be transferred to the uterus thus eliminating the chance for hemophilia in the child. Our Salt Lake City, UT PGD program routinely screens for many genetic disorders.

The risk of genetic disorders is directly related to female age. Women over 35 years of age are at higher risk for chromosomal abnormalities, which can lead to early miscarriage or conditions such as Down’s syndrome.

PDG- The Process

In PGD, one or two cells are removed from the embryo and genetically evaluated in a procedure known as a blastomere biopsy. The biopsy involves removing a small sample of the cells DNA. Initially, the cells have not differentiated and a biopsy can be taken, usually on day 3, without damaging the embryo. Results of the biopsy are typically available within 48 hours.  This means that the embryos transferred have the opportunity to develop to the blastocyst stage.

Using PGD, embryos are examined using fluorescent in situ hybridization (FISH) and/or the polymerase chain reaction (PCR). FISH involves labeling chromosomes with fluorescent tagged probes and examining them under a special microscope.  These tags allow gender determination, identification of missing or extra chromosomes, and translocations.

PGD using PCR creates multiple copies of specific identified areas of the chromosome and is used to screen for single gene defects. When the genetic disease is present in the parent, a copy of a segment of his/her gene can be used to make a genetic probe. This probe will “identify” the genetic disease if it is present in the embryo.

Our Salt Lake City Utah PGD program can currently screen for more than 120 specific genetic diseases such as Tay Sachs, cystic fibrosis, Fanconi anemia, fragile X syndrome, hemophilia A, and others.  As more genetic diseases are characterized, they are added to the list of those which can be screened.

Preimplantation Genetic Screening (PGS), Salt Lake City, UT

Preimplantation genetic screening (PGS) provides a means to screen embryos for abnormalities in chromosome number prior to uterine transfer in an IVF cycle.  PGS is also an extremely accurate method for identifying male and female embryos making gender selection, or family balancing, a scientific reality. Many couples want to experience the joy of raising children of both genders.

The risk of genetic disorders is directly related to female age. Women over 35 years of age are at higher risk for chromosomal abnormalities, which can lead to early miscarriage or conditions such as Down’s syndrome.

In the PGS procedure, one or two cells are removed from the embryo in a procedure known as a blastomere biopsy and genetically evaluated. The biopsy involves removing a small sample (single cell) of the embryos DNA. Initially, the cells have not differentiated and a biopsy can be taken, usually on day 3, without damaging the other cells and ultimately the embryo. The removed cell can then be used for PGS testing. Results of the screening are typically available within 48 hours.  This means that the embryos transferred have the opportunity to develop to the day 5 or  blastocyst stage.

Embryos have usually been examined using fluorescent in situ hybridization (FISH). FISH involves labeling chromosomes with fluorescent tagged probes and examining them under a special microscope.  These tags which are capable of evaluating (up to 12 pairs of chromosomes) allow for gender determination and identification of missing or extra chromosomes (in the 12 pairs evaluated).

Recently screening (2009) has become available through Gene Security Network for all 24 chromosome pairs in a single blastomere using state-of-the-art microarray chips. In addition they offer proprietary "parental support" testing to increase the accuracy of the results. Prior to testing the blastomere, cells are collected from the parents (or the egg or sperm donor) and a sophisticated bio information algorithm is used to incorporate parental data into the results on each cell.

Parental support helps correct errors produced during laboratory analysis, helps detect DNA contamination, assists in determining parental origin of trisomy or monosomy, provides detection of haploidy or polyploidy and assists in ranking the results for transfer to account for mosaicism. Test accuracy is thought to exceed 99%.

PGS does not guarantee a successful IVF cycle due to the fact that their are many factors that affect the chance for success. In addition, no test can guarantee the birth of a healthy baby. There are limitations to all PGS tests because any single cell analyzed may differ from genetically from the other cells in the embryo. This condition is called mosaicism. It is currently hypothesized that in some cases of mosaicism that the embryo can "self correct" and thus after PGS some embryos may not be chosen for transfer that may have developed into normal fetuses if they had been used. This situation although feasible is probably uncommon.

Aneuploidy screening should be discussed and considered in women over the age of 35, after recurrent pregnancy loss, or after previously unexplained failed IVF cycles. It can also be considered for decreasing the risk of having a child with aneuploidy.