A technique designed to evaluate whether any genetic problems might exist in embryos used in assisted reproductive techniques is still considered relatively new. But research like that released at a medical conference in Montreal recently is helping shed light on the possible benefits of the approach, known as preimplantation genetic diagnosis, or PGD.1
A Genetic Glance
PGD involves the genetic testing of embryos produced using in vitro fertilization (IVF). It is used to help physicians identify any possible genetic abnormalities in the embryos before they are transferred to begin a pregnancy.
The approach is designed for couples who face higher risks of having children with serious genetic disorders. It enables doctors to select embryos for implantation in the uterus that do not have such disorders, boosting the odds that these couples will have a child without a genetic abnormality.2
Without PGD, the only options facing couples with this higher risk have included prenatal diagnosis, terminating the pregnancy if the fetus is found to have the disease, facing the possibility of having an affected child, or avoiding pregnancy altogether.2
It's been more than ten years since the first pregnancies using PGD were reported, and some 1,000 infants have been born around the world using this technique. Among the genetic disorders diagnosed using PGD have included cystic fibrosis, muscular dystrophy, and sickle cell anemia.2
Using the technique, one or two cells are removed from an embryo, and analyzed for these genetic abnormalities.
Varying Pregnancy Rates
Among the studies released at the conference co-sponsored by the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society included one by experts at Reprogenetics, a genetics testing lab in New Jersey. It involved data on more than 4,000 PGD cases referred from 100 IVF centers around the country over a ten-year period. In 3,331 of the cases, the patients had embryos transferred. For patients in 2,540 of these cases, information was obtained on pregnancy results. There were 931 pregnancies and 640 deliveries. More than 300 of those pregnancies were still ongoing at the time the data were released, as well as 164 miscarriages that had been reported.
The researchers noted that the pregnancy rate varied widely depending on the IVF center reporting, as well as the diagnosis for each patient's infertility.
Benefit of PGD Found
Another study by Reprogenetics researchers involved more than 500 PGD cases referred from fertility clinics over the same 10-year period. The lab tested about 4,500 embryos during that period for genetic anomalies. Pregnancy information was available for 462 cycles. Of these, there were 138 pregnancies. So far, there have been 113 deliveries in this group, with 40 ongoing pregnancies and 15 miscarriages. The study investigators pointed out that before PGD, patients from these clinics miscarried 88% of their pregnancies; afterwards, the miscarriage rate plunged to just 9%, they wrote.
More PGD Data
Researchers at the Reproductive Genetics Institute in Chicago reported on 3,631 PGD cycles. Of these, nearly 800 cases involved PGD to detect single gene disorders and/or preimplantation human lymphocyte antigen (HLA) matching for couples at high risk of having a child with a genetically transmitted disease or those who already had a child needing matched stem cell transplantation from a sibling.
This unique screening resulted in the transfer of nearly 1,300 embryos resulting in 244 clinical pregnancies. Over 200 infants were born, and 35 pregnancies were still ongoing at the time the research was released.
Of the remaining 2,646 PGD cases cited in this study, detecting any chromosomal abnormalities was the goal for IVF patients with a poor prognosis. After testing, there were more than 2,100 transfers of 4,486 embryos. Five hundred fifty-four pregnancies resulted, 411 infants were born, and 91 pregnancies were still continuing.
Overall, the accurate rate using PGD at the institute was 99.5%, the researchers reported.
"We need to work to increase the availability of preimplantation genetic diagnosis and its use for patients for whom it is indicated," said William Gibbons, MD, President of the Society for Assisted Reproductive Technology (SART), in a statement. "Strategic use of PGD techniques can ultimately result in fewer pregnancies lost to miscarriage and a reduction in the number of multiple pregnancies when we can be sure we are transferring just one or two normal embryos."
1. Conjoint Meeting of the American Society for Reproductive Medicine 61st Annual Meeting and the Canadian Fertility and Andrology Society 51st Annual Meeting. 2005 Oct 15-19. Montreal, Quebec, Canada.
2. Genetics and Public Policy Center. Preimplantation Genetic Diagnosis (PGD). Available at: http://www.dnapolicy.org/genetics/pgd.jhtml.html.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
