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Is Genetic Screening Right For You?
November 15, 2012
Couples who have a history of recurrent miscarriage or unsuccessful in vitro fertilization (IVF) cycles may consider genetic testing for getting some answers.
Approximately 20% of pregnancies end in miscarriage and more than 50% of those are due to genetic abnormalities with the embryo. Known genetic disorders in either parent or recurrent miscarriage, usually more than 3 consecutive miscarriages, are cause for further examination.
Briana Rudick, M.D., of the Columbia University Center for Women’s Reproductive Care in New York, recommends patients who have genetic diseases or chromosome translocations to test their embryos using preimplantation genetic screening, though some fertility clinics are encouraging this practice for all IVF patients especially of advanced maternal age.
Types of Genetic Screening
The most commonly recognized term in regards to genetic screening is preimplantation genetic diagnosis (PGD). This procedure is used in conjunction with IVF and screens for a specific genetic disease that has suspected inheritance from the parents to the offspring. Preimplantation genetic screening (PGS) is a more inclusive term that examines risk of structural chromosome abnormalities, such as monosomy, trisomy, or translocations.
Previously, a limited number of chromosomes were testable. A procedure known as Fluorescent In Situ Hybridization (FISH) was used to remove a single cell from a Day 3 embryo, but could only test 10-12 chromosomes of the 23 pairs of chromosomes in a human cell. Despite this astonishing technology, many abnormalities remained undetected. Regarding the latest advances in genetic screening, Rudick says, “Advances include genetic testing at later points in embryo development, and movement towards better, more accurate testing. You can biopsy a day 3 or day 5 embryo. A technology called FISH used to be the way that we detect chromosome abnormalities in the cells that we biopsy, but this is increasingly being replaced with a newer technology called array CGH.”
CGH, or Comparative Genomic Hybridization, shows a much bigger picture of genetic makeup- all 23 chromosomes at full length. Array CGH is an accelerated protocol which produces genetic screening results in 24 hours. How’s that for efficient?
What Genetic Screening Looks For
These genetic screening procedures will detect abnormalities and provide insight as to the potential cause of past miscarriage or failed cycles. It will also help fertility doctors to predict an embryo’s ability to implant and develop into a healthy pregnancy. Rudick says: “By knowing if [an] embryo has a normal number of chromosomes, you can weed out the abnormal ones [and] not transfer those abnormal ones into the uterus. Alternatively, if both parents carry some kind of specific mutation, you can look for the presence of that mutation in the embryo.”
Results and Risks of Genetic Screening
Dr. Rudick cautions patients against transferring abnormal embryos for the unlikelihood that they will develop into healthy pregnancies. If repeated abnormal results present, it might be time to discuss donor egg options with your fertility doctor.
The risks of genetic screening biopsy to the embryo are small, and accuracy rates are rising with more advanced technologies. It is best to discuss genetic screening with your doctor to determine if it is an option for you. Alternatives include amniocentesis and chorionic villus sampling later in pregnancy, though they cannot be used to detect causes of early pregnancy loss.