Screening the embryos of an older woman undergoing in vitro fertilization (IVF) for genetic defects — a procedure known as preimplantation genetic screening — does not boost her chances of pregnancy and appears to worsen her chances, Dutch researchers say.
But soon after the study was published in the July 5 issue of The New England Journal of Medicine, it was criticized by some reproductive technology experts, who say the researchers' scientific techniques weren't up to standards.
Preimplantation embryo screening is offered routinely to "older" women ages 35 and up at some IVF centers. In the screening technique, which costs about $3,000 to $5,000, a single cell is aspirated from each embryo to check for chromosomal abnormalities. The embryo isn't transferred if abnormalities are present. The screening technique evolved as a logical extension of preimplantation genetic diagnosis, offered to couples with a known genetic defect.
But the new Dutch study shows that pregnancy rates were lower in the women who got the test. While 25% of those who got the test got pregnant, 37% of those who didn't get it became pregnant.
"Preimplantation genetic screening is an expensive technique that is very frequently offered to women of advanced maternal age under the statement that it will increase pregnancy rates," says researcher Sebastiaan Mastenbroek, M.Sc., a Ph.D. student at the Center For Reproductive Medicine at the Academic Medical Center in Amsterdam. Based on the new study results, he says, "PGS is not the best option for these women. A regular IVF treatment without PGS provides them with a higher chance of pregnancy."
In the study, Mastenbroek and colleagues evaluated 408 women undergoing IVF at several Dutch centers from May 2003 through November 2005. They assigned 206 to the genetic screening group and 202 to a group that not get the screening.
Besides a lower pregnancy rate, those who got the embryo screening also had a lower live-birth rate — 24% vs. 35%, the researchers found.
Drawing conclusions from the Dutch study would be premature, critics say. They found fault with the research for a number of reasons.
"This research team is inexperienced," says Santiago Munne, Ph.D., a member of the board of directors for the Preimplantation Genetic Diagnosis International Society, a Chicago-based organization that coordinated research, education, and training in the technique.
Munne and other critics say that inexperience affected the results. For instance, 20% of the embryos tested came up with "undetermined" results, with the researchers unable to term them normal or abnormal. "Experienced centers typically have a 5% indeterminate rate," Munne tells WebMD.
The undiagnosed embryos were transferred to the women, resulting in an implantation rate of 6% compared with the higher 14.7% implantation rate in the group of patients whose embryos did not have biopsies, he says.
"In our study, all biopsies were performed on the third day after insemination, which is very normal in the case of preimplantation genetic screening," Mastenbroek responds.
"Our results are in line with all other data available in the scientific literature," he adds. "A beneficial effect in terms of ongoing pregnancy has never been shown for PGS. Lower ongoing pregnancy rates have been shown before, but this outcome was significant in our trial since this is the largest randomized trial available today."
Now, he says, his team is investigating why the technique was ineffective.
In an editorial accompanying the study, John A. Collins, M.D., a physician at McMaster University in Hamilton, Ontario and Dalhousie University, Halifax, Nova Scotia, Canada, puts the results in perspective: "he results suggest that for every nine women who are 35 to 41 years of age who plan three cycles of IVF or IVF and intracytoplasmic sperm injection, there will be one more live birth if pre-implantation genetic diagnosis for [abnormalities] is not performed."
In an e-mail interview, Collins tells WebMD that the new study results are "convincing most people in the field that PGS has no value in screening infertile women over 35 undergoing IVF."
In his editorial, Collins advises that the preimplantation screening not be done solely due to a woman's age.
By Kathleen Doheny
Reviewed by Louise Chang, M.D.
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