One is the healthiest number: method may identify best embryos for in vitro fertilization.
Such research could improve the chance a woman will get pregnant when only one embryo is transferred to her womb. Currently, many fertility clinics in the United States implant two or more embryos created during in vitro fertilization, often resulting in pregnancies with multiple "test tube babies." Pregnancies with multiples carry risks for mother and child.
These risks include premature birth, low birth weight, cerebral palsy and other disabilities, as well as infant death and pregnancy complications.
"The goal is to have healthy children one at a time," says David Ball, an embryologist at Seattle Reproductive Medicine.
But many people who have fertility problems are willing to have multiple embryos implanted in order to increase the chance of getting pregnant. "Patients look at it as they're paying a lot of money and they want to be sure it works," Ball says. "They'd rather have two [babies] than none."
Doctors cannot definitively distinguish which embryos will result in pregnancy and which will not, says Richard Paulson, a reproductive medicine specialist at the Keck School of Medicine of the University of Southern California in Los Angeles.
Fertility clinics examine embryos under a microscope and discard those that have obvious abnormalities, but several labs are moving toward molecular methods to identify the best embryo from the bunch. Paulson, who was not involved in the study, is testing the nutrient solution in which embryos are grown to see if healthy embryos make substances that distinguish them from unhealthy embryos.
In the new study, Gayle Jones and her colleagues at Monash and in Athens, Greece, extracted cells from embryos made during in vitro fertilization. The researchers could safely remove up to 20 cells from the outer layer of cells in a 5-day-old embryo. The embryos were then transferred to their mothers' uteruses. Some of the embryos developed into healthy babies. Others failed to implant in the womb or were not carried to full term.
DNA fingerprints of cheek swabs or umbilical cord blood from the full-term babies were matched to DNA fingerprints from the embryos to determine which embryos had been viable--offering direct feedback about which embryos produce healthy babies, Paulson says.
The researchers found that viable embryos turned on genes that encode cell adhesion molecules and cell communication proteins, the researchers reported online May 13 in an advance publication of Human Reproduction. Both types of molecules are likely to be important for the embryo to latch on to the uterine wall and grow.
The technique is still experimental and Jones and her colleagues aren't saying which genes are important for viability. "We have no confidence that we've found a predictive set of genes yet," Jones says.
Whittling the possible candidate genes down to a manageable number, fertility clinics could do viability tests to find optimal embryos to transfer. "We will be able to give clinics and patients confidence to accept single embryo transfers without affecting the pregnancy rate," Jones says.
"I don't think this is ready for prime time," Paulson says, "but I do think it's a very powerful research tool."
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|Title Annotation:||Body & Brain|
|Author:||Saey, Tina Hesman|
|Date:||Jun 7, 2008|
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