Preimplantation Genetic Diagnosis
Testing your embryo before it's in utero
Who Can Benefit from PGD?
There are four common reasons for requesting PGD. Like Amanda, some couples need to screen embryos for single gene disorders that cause specific diseases like cystic fibrosis, hemophilia, sickle cell, Duchenne muscular dystrophy, and Tay Sachs, just to name a few. Amy Jones, MS, ELD, director of preimplantation genetic testing at Nashville Fertility Center, where Amanda underwent IVF and PGD, says, “To test for a single gene disorder, you have to have a known genetic condition in the family.”
Couples with a history of miscarriage are sometimes good candidates for PGD to test for aneuploidy, a condition where an embryo contains too many or two few chromosomes. Chromosomes are strands of DNA found in every cell. The typical human has 46 chromosomes. Extra or missing chromosomes result in birth defects like Down syndrome and Turner syndrome. This situation, aneuploidy, accounts for up to 60 percent of early miscarriages because a woman’s body recognizes the abnormal embryo and rejects it.
Lianne from New Jersey is a perfect example. Although she gave birth to a daughter in 2004, she suffered multiple miscarriages before and afterward. After one of the miscarried fetuses tested positive for Downs syndrome, doctors at IVF New Jersey suspected that aneuploidy was the cause. “I didn’t have a problem getting pregnant,” Lianne says, “I had a problem holding the babies.” Her physicians were right. When she tried IVF in 2007, they removed 10 eggs. Seven of them fertilized, but PGD revealed that five of the seven embryos showed chromosomal abnormalities. The two normal embryos were implanted, one continued to develop, and the family welcomed a healthy baby nine months later.
PGD can also prevent miscarriages caused by a chromosomal translocation; when a section of one chromosome swaps places with a section of a different chromosome. Like aneuploidy (wrong number of chromosomes), translocation (mixed up parts of chromosomes) can result in the birth of a child with physical and mental impairments, but it more often causes miscarriage.
One last and very rare use of PGD is to help families have a child who has the potential to save the life of another, seriously ill, family member. A small number of diseases are best cured with bone marrow from a relative who is also a human leukocyte antigen (HLA) tissue type match. Jones explains, “If the couple has a child with a disease that can be cured with bone marrow from an HLA compatible relative, they want to create a child that is disease free and an HLA match.” But she says that it’s not a sure thing because fewer than 20 percent of embryos a couple creates are an HLA match for a sibling or other relative.
Look Too Hard and You’ll Find a Problem
Although preimplantation genetic diagnosis has been available for a decade, it’s still only performed on about 5 percent of IVF patients because it’s not particularly useful for couples with no history of genetic conditions. In fact the American Society for Reproductive Medicine (ASRM), the national governing body for assisted reproduction, recommends against using the technology to screen IVF embryos for any and all abnormalities without a preexisting reason. “When you’re looking for a specific disease, PGD is accurate. Misdiagnosis comes from a full genetic screening. It doesn’t ensure a healthy baby” says Williams. He adds, “Pulling a cell from an embryo for no reason isn’t smart thing to do. It can harm the embryo.”
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