A new study that tested the rigidity of an hour-old fertilized egg may result in a more accurate way for physicians to choose the best embryos during in vitro fertilization. Stanford University researchers concluded that the success of IVF lies in how viable the fertilized egg is.

In the study, published Wednesday in Nature Communications, researchers applied a small amount of pressure to mice eggs with a small pipette about an hour after fertilization. They then recorded how much each egg deformed. The embryos were placed in a standard nurturing liquid and reexamined at the blastocyst stage, according to a news release. According to researchers, the eggs that had provided a certain range of push back were more likely to produce healthy, symmetrical embryos.

Researchers were then able to create a predictive computer model based on the egg’s squishiness that could predict with 90 percent accuracy whether a fertilized egg would grow into a well-formed blastocyst.

The embryos were transferred to female mice, and those 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 involved stiff tumors or tissues, our colleagues have been surprised that we can gain so much information from this simple little mechanical test,” Dr. Barry Behr, director of Stanford’s IVF laboratory, said in the news release. “It is still surprising to think that simple squeezing an embryo the day it was fertilized can tell you if it will survive and ultimately become a baby.”

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