Genetic screening test helps older moms decide on implanting embryos
posted by: Guest Blogger
An increasingly popular genetic-screening test is offering new hope to older women trying to get pregnant through in-vitro fertilization.
The procedure, offered by three Colorado fertility clinics, examines cells from 5-day-old embryos to determine which are likeliest to become healthy full-term babies.
Fertility specialists say the new test, which evaluates a larger number of chromosomes than other practices, is significantly more promising for women in their late 30s.
And it might be safer for embryos, which have been more routinely tested at a fragile three days.
“It is as if we are turning back the biological clock for women ages 38 to 42,” says William Schoolcraft, director and founder of the Colorado Center for Reproductive Medicine.
For such women as Rachel Johnston, the new test was a godsend. She struggled with fertility problems for years before traveling to Colorado last year specifically for the screening test offered at Schoolcraft’s clinic. Two months ago, Johnston, 39, gave birth to twins Toby and Zoe.
“I was much more comfortable being able to confirm that the embryos truly were chromosomally normal,” said Johnston, a New York City accountant.
“Of 11 embryos, six came back normal. We chose two, to have twins, and we still have four frozen. We don’t know yet if we’ll have another baby. Twins are more than enough for us at the moment.”
The screening, known as comparative genomic hybridization, doesn’t guarantee pregnancy, but physicians are encouraged by its early success.
The Center for Reproductive Medicine, which began offering the procedure in 2007, reports that of 269 patients who used it, 197 pregnancies resulted. Of those, there were 172 healthy babies born, 17 current pregnancies and eight miscarriages.
Two other local infertility- treatment clinics — Conceptions Reproductive Associates of Colorado and the Reproductive Medicine and Fertility Center — offer the screening.
The procedure will be among the subjects discussed this week at the American Society for Reproductive Medicine conference at the Colorado Convention Center.
“For sure, this will get some buzz,” said Mandy Katz-Jaffe, research director at the Center for Reproductive Medicine. She will be among the presenters at the conference.
Some of that buzz might include questions about whether the procedure — which enables testing not just for health problems but also for detailed physical characteristics because the embryo is more fully developed — could open the door to ethical questions.
Hopeful parents already can choose whether to implant a boy or a girl. As genetic screening becomes more sophisticated, will they be able to choose an embryo whose eyes will be blue and handpick other physical traits?
So far, the information has not been used here to advise parents on matters beyond gender and health, the clinics say, though it is possible that could happen elsewhere.
And still, some are concerned about the fate of embryos that don’t measure up.
“They were screening before for Down syndrome, so the issue really becomes whether they’re informing the family that they have an embryo that has Down syndrome, or are they discarding those embryos in the lab,” says Edward McCabe, executive director of the Linda Crnic Institute for Down Syndrome at the University of Colorado Medical School.
“I’m a geneticist, and I feel that isn’t the lab’s decision,” McCabe says. “There should be nondirective counseling: Let it be the couple’s decision and not ours.”
Fertility specialists say they do allow prospective parents to make those decisions.
“This isn’t eugenics,” says Mark Bush, an associate at Conceptions.
Genetic screening of in-vitro fertilizations has been available since the early 1990s, when the test relied upon a cell taken from a 3-day-old embryo. That procedure, which examined seven to 11 chromosomes to look for abnormalities including Down syndrome, still left parents with doubts.
A 3-day-old embryo has only eight cells, and those can evolve into any type of cell in the embryo or placenta. Nobody knows if taking one of those cells might damage the embryo.
But at 5 days old, the cells have multiplied drastically — to between 50 and 100 — and the placenta and embryo have formed. Embryologists can choose several cells from the placenta instead of the embryo.
Then they screen those cells and examine all 23 pairs of chromosomes, looking for abnormalities, some of which might result in implantation failure or miscarriage.
“If you grow the embryo to Day Five, and I can get six cells from the early placenta, that information is cleaner and more accurate than the cells from a three-day embryo,” Bush said. “If there are four embryos, I can tell the couple, ‘You have a normal girl in dish one, a normal boy in dish two and a trisomy — an indicator of Down syndrome — in dish three.’ ”
Pre-implantation genetic screening is expensive, about $5,000 on top of a clinic bill that may already top $15,000. It is not automatically covered by health insurers.
Still, many patients who have had miscarriages and conception problems are willing to pay for a test that may mean the difference between another miscarriage and a chance to finally hold their own baby.
One downside: Sometimes none of the embryos is viable. That’s also valuable information, Bush says.
“If I can tell her that all the embryos were abnormal, then she’s convinced. She can say, ‘You gave me a shot and proved that my eggs aren’t working,’ and the couple won’t have to go through the miscarriage business,” he said.
-By Claire Martin, Photo Wageningen Tissue Culture Center