We now offer preimplantation genetic diagnosis (PGD) of embryos to couples undergoing IVF. Through PGD, patients can now determine if an embryo will be affected by a certain genetic abnormality prior to its transfer and implantation in the uterus. PGD was first introduced over a decade ago in the UK during the late 1980's. The first PGD baby was born in 1989 and now this procedure is recommended for women over 35 years of age and for couples who are at risk for passing a genetic or sex-linked genetic disease to their offspring.

The couple will undergo In Vitro Fertilization to create several embryos for the genetic testing. Three days after the eggs have been fertilized with sperm, one or more blastomere (cells) is extracted from each embryo using a pipette. The removal of these cells is unlikely to affect the developing embryos because the cells have not begun to differentiate yet. By removing the cells, the growth of the embryo has been delayed for a few hours, but will continue with its normal development. This blastomere is then subjected to DNA analysis. The cells are analyzed
using fluorescence in-situ hybridization or FISH technique. Small pieces of
DNA are matched for the chromosomes that are being tested, called probes.
Each probe is labeled with a different fluorescent dye. The fluorescent
probes are applied to the cell and attached to the chromosomes. Using a
fluorescent microscope, the number of chromosomes of each type (color) is
counted in that cell. The geneticist can distinguish between normal and
abnormal cells. Results are known within twenty-four to forty-eight hours.
One to four healthy embryos are transferred into the woman's uterus and the
remaining embryos are cryopreserved.

• Any woman, age 35 years or older. It is currently estimated, that women who are 35 years of age at the time of delivery have a 1/384 chance of carrying a Down syndrome fetus. The risk of an aneuploidy (other chromosomal disorder) fetus is 1/204. The ratio significantly decreases and therefore the risk increases, for every year over the age of 35.
  
  
• Any person who may have a sex-linked (X) genetic disease such as duchenne muscular dystrophy.
  
  
• Any woman who has previously had a pregnancy with a chromosomal abnormality.
  
  
• Men or women who have a chromosomal translocation. A man or woman, even though they themselves are phenotypically (chromosomally) normal, may be carriers of abnormal chromosomes and may produce abnormal children.
  
  
• Couples who have had multiple IVF cycles without a resulting pregnancy.
  
  
• Any woman who has had repeated miscarriages due to chromosomal abnormalities.

• There is an increased chance of having a normal baby.
  
  
• Usually genetic testing is done when the fetus is twelve to sixteen weeks old using chorionic villi sampling (CVS) or amniocentesis. The expectant parents must then wait for approximately three weeks to find out the results of these tests. With PGD, the genetic testing is done prior to implantation, saving the intended parents the stress of deciding to keep or abort the fetus. Because PGD is 90% accurate, it is recommended that CVS or amniocentesis be performed at the appropriate time for confirmation that the developing fetus has normal chromosomal make-up.
  
  
• Abnormal embryos have a significantly decreased survival rates compared to normal embryos. Therefore there is an increase in the pregnancy rate by not implanting those embryos that have abnormal chromosomes. Abnormal chromosomes in the developing fetus cause approximately 50% or more of the cases of miscarriages. By transferring only normal embryos, the miscarriage rate is significantly reduced.
  
  
• If only normal chromosome embryos are transferred, the pregnancy rate increases and the miscarriage rate decreases. The chance of inducing a pregnancy termination following a CVS or amniocentesis is decreased.
• If PGD becomes widespread, the incidence of many genetic diseases would be reduced.
  
  
• PGD could significantly reduce medical costs with the decrease in medically challenged children being born. Treatment of some genetic diseases can cost hundreds of thousands of dollars over the lifetime of a single individual.
  
  

More than two hundred diseases including single gene defects as well as sex-linked diseases can be evaluated using the PGD technique. These diseases include, but are not limited to:

• duchenne muscular dystrophy 
  
• hemophilia A 
  
• fragile X syndrome 
  
• retinitis pigmentosa 
  
• tay sach's disease 
  
• genetic abnormalities that may be detected and include aneuploidies XY,
  13, 15, 16, 17, 18, 21 and 22 
  
• cystic fibrosis
  
• lesch-nyhan syndrome 
  
• 6-phosphate dehydrogonase deficiency 
  
• testicular feminization 
  
• fabry's disease vitamin D-resistant rickets 
  
• psuedohypoparathyroidism 
  
• incontinentia pigmenti 
  
• focal dermal hypoplasia 
  
• orofaciodigital syndrome 
  
• hyperammonimia due to ornithine transcarbgomylate deficiency 
  
• nephrozine diabetes insipidus
  
  

There is a 90% success rate with an even higher success rate on some PGD testing. There is an error rate of 10%, which would include false negative and false positive results. There is also a possibility that cells from the same embryo might have a differing number of chromosomes. It is therefore, possible that the cell for PGD testing is normal, while another cell in the same embryo is abnormal. Due to the chance of misdiagnosis as well as the presence of abnormal chromosomes that cannot be tested at this time, it is recommended that prenatal testing of CVS or amniocentesis be done at the appropriate time.