Stanford researchers find new way to check on embryo viability

Researchers at Stanford University have devised a new way, simple as choosing a ripe piece of fruit, to select the right fertilized embryo for in vitro fertilization (IVF).

Stanford bioengineers and physicians said the squishiness of an hour-old fertilized egg can predict its viability. The way to do it: just give it a squeeze. If it is too firm or too soft, it might not be good. The sweet spot in between is just right.

In a study published in Nature Communications, the researchers said the technique is more accurate than current methods and may improve the success rate of single-egg IVF, which consequently may improve the prognosis for both mothers and babies.

With current IVF embryo screening, five or six days after an egg is fertilized with sperm, once the embryo has reached the 60-100-cell blastocyst stage, the embryos' morphology and the rate at which cells have been dividing are evaluated. The best-looking embryos that have been dividing at the "best" rate are then selected for transfer.

Another choice is to pluck a few cells from the blastocyst for genetic testing, which can increase the odds of choosing a successful embryo. But the invasive procedure can stress the embryo, even though the sample is taken from cells that will eventually form the placenta.

In either case, the results are uncertain, and the 70 percent failure rate means that doctors typically implant multiple embryos into a mother's womb, in hope that one will take hold.

"A lot of twins are born because we don't know which embryos are viable or not, so we transfer several at one time," said lead-author Livia Yanez, a bioengineering PhD student at Stanford. "This can increase the risk of neonatal mortality and cause complications for babies and the mothers.

Her idea for a solution is a mechanical test that could "ascertain embryo viability well enough that doctors could implant just one embryo and have a very good feeling that it would be viable."

Following an anecdotal tip from Barry Behr, the director of Stanford's IVF laboratory, that some eggs are squishier than others, the researchers began investigating whether this had something to do with the fertilized egg's ultimate development potential.

Using a small pipette, they applied a small amount of pressure to mice eggs an hour after fertilization and recorded how much each egg deformed. They placed the embryos in a standard nurturing liquid and reexamined them at the blastocyst stage. At this point, the eggs that had provided a certain range of "push back" were more likely to produce healthy-looking, symmetrical embryos.

This data were built into a predictive computer model that, based only on the egg's squishiness, can predict with 90 percent accuracy whether a fertilized egg will grow into a well-formed blastocyst.

Next, the researchers transferred the embryos to mother mice. Embryos classified as viable based on squishiness were 50 percent more likely to result in a live birth than embryos classified as viable using conventional techniques.

"Although cancer and other diseases involve stiff tumors or tissues, our colleagues have been surprised that we can gain so much information from this simple little mechanical test," said David Camarillo, an assistant professor of bioengineering. "It is still surprising to think that simply squeezing an embryo the day it was fertilized can tell you if it will survive and ultimately become a baby."

They repeated the experiment with fertilized human eggs and found that the rigidity assessment could foretell whether the embryo would reach a healthy blastocyst stage with 90 percent accuracy. They are ramping up viability testing in patients.

"From a clinical perspective, once confirmed, the benefit is immense in that it could give us a proxy of viability of the embryo in the blink of an eye, and from that information we can manipulate the patient's cycle in order to improve success," said Behr, a co-author on the study. "It's very exciting work, and I'm happy to be a part of it." Endit