Gene Test Raises Pregnancy Chance
But study involved only one woman
THURSDAY, Dec. 13, 2001 (HealthDayNews) -- Australian researchers are reporting the first healthy birth using a combination of in vitro fertilization (IVF) and a new version of genetic analysis that helps detect chromosomal abnormalities linked to pregnancy loss.
"The procedure permits the selection of embryos that are normal, at least with respect to the chromosomes analyzed, for transfer to the patient and may lead to an increased rate of implantation and a decreased rate of embryo loss after implantation," say the study authors in a report in a recent issue of The New England Journal of Medicine.
But the study only involved one woman, and at least one critic questions giving so much credit to the method of genetic analysis.
In IVF, sperm and egg are fertilized in a laboratory dish where the resulting embryo begins to grow. When it grows to eight cells, it is implanted into the uterus, where hopefully it attaches to the lining to begin a pregnancy.
However, when the embryo is in some way defective -- usually the result of a chromosomal or genetic abnormality -- it often is miscarried. Experts say a new type of genetic analysis, called Comparative Genomic Hybridization (CGH), may detect which embryos are normal ahead of time and cut down on miscarriages.
"Genetic analysis has great potential as a diagnostic tool and may, in the future, be particularly helpful for women who are subject to chronic pregnancy loss," says Dr. Jaime Grifo, director of the Division of Reproductive Endocrinology for the IVF Program at New York University Medical Center. Grifo was not a researcher on the study.
But while an embryo that clears the test is less likely to be defective, Grifo stresses the results are not 100 percent accurate. Miscarriages occur for lots of reasons, and "not every reason is linked to chromosomal abnormality," he says.
Dr. Zev Rosenwaks, director of the Center for Reproductive Medicine and Infertility at the Weill Medical College of Cornell University, says the report is important because it used genetic analysis in a new way -- to study the complete set of chromosomes with a single biopsy, thereby increasing the chance of discovering an abnormality.
"The reason this was a worthwhile article is that it presented a case where they successfully applied CGH to all 23 chromosomes and were able to show that the embryo they put in was normal," says Rosenwaks.
The study, by doctors at Melbourne IVF and Murdoch Children's Research Institute, involved a 38-year-old Australian woman with a seven-year history of unexplained infertility. She was given fertility drugs to stimulate production of eggs, which were retrieved surgically from her ovaries. The eggs were combined with sperm in the laboratory, resulting in eight fertilized embryos. In four separate IVF transfers, the embryos were implanted into her uterus. She didn't get pregnant with any of them, report the study authors.
The woman underwent a second round of fertility drug treatment, from which she produced 15 eggs. Nine of those eggs, thought to be viable, were tested using a system known as "fluorescence in situ hybridization," a less sophisticated way than CGH of examining eggs for chromosomal abnormalities. Of the nine embryos, two looked normal and were implanted into the woman's uterus. Still no clinical pregnancy resulted.
Finally, a third round of fertility drugs stimulated the production of yet 14 more eggs. Using a method known as intracytoplasmic sperm injection, the sperm was deposited directly into each of the eggs, and they then were placed in a laboratory dish to grow. Eleven embryos resulted, which were then frozen and tested using the more sophisticated CGH system of analysis.
Of the 11, all but one tested positive for chromosomal abnormalities. That one, seemingly healthy embryo was implanted into the woman's uterus, and the researchers report the pregnancy was successful.
"The transfer of a single embryo identified as normal by this technique resulted in the birth of a normal, full-term infant in a patient with a seven-year history of unexplained infertility," say the authors.
Not everyone, however, is convinced that CGH was solely responsible for the pregnancy's success.
"I'm not certain that the reason this patient got pregnant was because they did this. A woman who has two failures of IVF doesn't get pregnant all of sudden because they put in a normal embryo; this doesn't make sense to me," says Rosenwaks.
However, he says, the system has value for future use.
"CGH is well worthwhile and is something that will be applicable in the future; it's just that right now, most clinics cannot do it so easily, and it's still considered in development," says Rosenwaks.
Grifo agrees: "It's a good step forward, but based on what we know right now, the application of this technology is still subject to limitations and has no broad, sweeping clinical application for most patients."
What To Do
To learn more about in vitro fertilization visit the Genetics and IVF Institute.
For more about treatments for chronic miscarriage, click here.
To learn more about preimplantation genetic testing , click here.