Your husband’s eye color. Your wife’s dimple. Each partner contributes unique cells that hold the characteristics that a new, unique human being will inherit and develop. That isn’t always a good thing. Linda Clark is a carrier for a genetic disorder called Marfan syndrome. The syndrome can make pregnancy risky. It also can suddenly kill seemingly healthy young people. People in their prime. That was reason enough to choose PGD – or preimplantation genetic diagnosis for her embryos.
Preimplantation Genetic Diagnosis is not simply one test, but a combination of techniques administered by highly skilled embryologists, scientists who specialize in embryo development. It allows an embryologist to view the genetic makeup of a single cell from an embryo created with IVF. PGD can provide answers to hopeful parents-to-be in several different circumstances. "If you have a chance to give a child the best life you can," she said, "Most people - if they really think about it - would choose to do that," said Linda Clark in an interview with the St. Louis Dispatch.
How it works
An embryo has to first be created in the lab through IVF. On day 3 of its development, a cellular biopsy is done on one or more cells, called a blastomere. At that stage of development, removing a cell generally doesn’t harm the embryo. Most embryos have between four and 12 distinct cells. The cell has to be examined with the fluorescence in situ hybridization (FISH) or DNA analysis.
Detecting chromosome glitches
Preimplantation Genetic Diagnosis is most frequently recommended for patients who are at risk for genetic disorders such as cystic fibrosis, Tay Sachs disease, muscular dystrophy, and sickle cell anemia. The transmission of a chromosome abnormality to an embryo can result in a low implantation rate, miscarriage, or the birth of a baby with a genetic disorder.
Preimplantation Genetic Diagnosis doesn’t guarantee a healthy baby. You can get false positive results when using PGD for screening for chromosome abnormalities. "False positive results are when we say that the embryo is abnormal, but it is truly normal," explains Susan Sarajari MD, PhD of the Huntington Reproductive Center.
Selecting for Sex
Preimplantation Genetic Diagnosis is 99% accurate for sex selection. However, many clinics will not do PGD solely for family balancing. In fact, the professional membership group for fertility specialists, the American Society for Reproductive Medicine (ASRM) has said that PGD for sex selection is only acceptable to avoid the birth of children with genetic disorders, and not for any non-medical reasons. These are just guidelines and fertility specialists are not governed by these recommendations.
Should I or Shouldn’t I?
Preimplantation Genetic Diagnosi isn’t the right choice for everyone. Dr Yannis Giakoumakis MD of the Mediterranean Fertility Center and Genetic Services suggests PGD may be helpful if:
- Are you a woman over 35
- Have you experienced several miscarriages
- Have you had a prior pregnancy with a chromosome abnormality
- Have you experienced several failed IVF cycles
- Has conceiving been difficult due to a low sperm count
- You or your partner carry a balanced structural chromosome rearrangement
- You or your partner carry an X-linked genetic disease such as hemophilia or Duchenne Muscular Dystrophy Steady hands
Whether or not Preimplantation Genetic Diagnosis does damage to the embryo may very well be up to the person in the back of the lab. The skill of embryologist is very important. You need to have someone very experienced doing that initial biopsy – at least 75-100 a year.
"My first RE really discouraged PGD, and it was only after I moved on to another clinic that I found out that the first clinic's stats were losing 1 in 4 embies to the initial biopsy. No wonder that RE discouraged me from using PGD! A very experienced (and skillful) person doing the biopsy may lose 1 in 100!," says Anne, who chose PGD and delivered healthy twins. There is some risk, estimated to be below one percent, of accidentally damaging the embryo in the biopsy process.
In a poll on ivfconnections.com, a quarter of the respondents indicated their health insurance paid for Preimplantation Genetic Diagnosis, while 75% said their health insurance would not do so. The reason you want PGD is sure to play a role, so find out what’s covered before you biopsy those embryos – the price tag is a hefty $20K on top of the oh-so-pricey IVF process.
What do I do?
It’s expensive, you might risk damaging your embryo, you might reject an embryo that tests positive for a problem it doesn’t have. It isn’t an easy decision to make. As embryologist Michael Tucker, PhD explains, "As with many things in life, patients and physicians must do a cost-benefit assessment based on the risk to the embryo weighed against the medically-driven reasons for performing PGD." A helpful resource when making this decision is a genetic counselor. Genetic counselors are trained to evaluate family history and medical records, order genetic tests, evaluate the results of this investigation, and to help parents understand and reach decisions about what to do next.
- ESHRE Preimplantation Genetic Diagnosis Consortium ‘Best practice guidelines for clinical preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS)
- A.R. Thornhill, C.E. deDie-Smulders, J.P. Geraedts, J.C. Harper, G.L. Harton, S.A. Lavery5, C. Moutou, M.D. Robinson, A.G. Schmutzler, P.N. Scriven, K.D. Sermon and L. Wilton
- Human Reproduction vol. 20 no. 1 © European Society of Human Reproduction and Embryology 2004.