In vitro fertilization (IVF) treatments can be expensive and time-consuming, so parents want to pick the embryos with the best chance of success. Researchers have now discovered a potential test to help them determine embryo viability: the squishiness test.
The study comes from bioengineers at Stanford University who published their results in the February 24th issue of Nature Communications. They wanted to find a way to improve how technicians choose the embryos with the best chance of survival in fertility treatments.
Currently, fertility technicians have a couple of ways of guessing which embryos are most likely to result in a successful pregnancy. One way is to examine an embryo five or six days after they have fertilized the egg with sperm. At this blastocyst stage, the embryo has about 60 to 100 cells, and scientists examine the appearance of the embryo as well as its cell division rate. The embryos that appear to look the best and appear to be dividing well are then selected to be implanted into the mother. The second method involves removing a few of the embryo’s cells and performing genetic tests. Although this can give technicians a better idea of the health of the embryo’s genetic makeup, the procedure is invasive and can cause stress to the embryo, potentially reducing its survival chances.
To compensate for the uncertainty about embryo viability, fertility treatments will usually involve placing more than one embryo inside the mother’s womb. Although this can increase the chance that the mother will have a successful pregnancy from one of these embryos, it can also mean twins, triplets, or more. The parents may not be prepared to have multiple children at once, and it can also mean greater chance of problems such as the children being born prematurely or other complications.
Since the current IVF methods can result in a 70 percent failure rate, researchers are looking for even better ways to increase the odds of a successful pregnancy. Some researchers had noticed that some eggs are squishier than others, and the researchers in the current study decided to find out if this could be an indicator of embryo viability.
The study involved looking at mice eggs. An hour after fertilization, the researchers used a small pipette to apply a little pressure to the eggs and noted how much each egg deformed under this pressure. The researchers then came back to the eggs when they had reached the blastocyst stage. Using one of the existing methods of determining viability, the researchers looked at whether the embryos at this stage were symmetrical and healthy-looking. The scientists found that the eggs which were less easily deformed with the squishiness test were more likely to develop into the healthy-looking embryos. Once the researchers put their data into a computer, they were able to predict whether a particular fertilized egg would grow into a healthy-looking and symmetrical blastocyst, with 90 percent accuracy.
The next step was to transfer the embryos into mothers and assess whether they resulted in a live birth. The results showed that eggs that had passed the squishiness test were 50 percent more likely to lead to a live birth than embryos that the researchers had determined were viable using the existing techniques.
After the success with their method in determining the viability of mouse eggs, the researchers turned to human eggs. They found similar results when looking at which eggs would result in healthier-looking blastocysts, with 90 percent accuracy. The next step will be to determine whether the eggs that pass the squishiness test will lead to successful pregnancy in humans as they did in mice.
The researchers liken their technique to squeezing fruit to determine its freshness, however they do not know for certain why the technique works in fertilized eggs. The scientists speculate that since genes are involved in DNA repair, managing cell division, and aligning replicating chromosomes, as well as egg hardening after fertilization, any problem with the firmness of the egg could indicate general genetic problems.