Fertilized human egg emits microscopic flash of light

When you meet someone who ignites your passion, it can feel like fireworks are going off. New research by Northwestern University researchers, published in the journal Scientific Reports, shows that when human sperm meets an egg, it can also set off sparks.

When an egg is fertilized, the rapid release of zinc creates a spark

In vitro fertilization is seen in this file photo. The size of 'zinc sparks' has been linked to an egg's quality and ability to grow into a viable embryo, which could improve the selection process for in vitro fertilization. (Dr. Thomas Hannam)

When you meet someone who ignites your passion, it can feel like fireworks going off. New research by Northwestern University researchers, published in the journal Scientific Reports, shows that when human sperm meets an egg, it can also set off sparks.

For the first time, scientists have proven that when a human egg is fertilized, it releases what are called zinc sparks. Upon fertilization, calcium increases and zinc is rapidly released. When this happens, the zinc joins itself to small, light-emitting molecule probes. In other words, it creates a microscopic flash of light.

The scientists were unable to fertilize eggs with sperm for this study due to legal issues surrounding research with human embryos. Instead, they injected the eggs with a sperm enzyme, triggering the egg activation process and causing the increase in calcium and release of zinc.

Zinc sparks had previously been seen in animal studies, but the discovery that they also occur in humans could have significant ramifications for assisted reproduction technology. This is because the animal studies, where the eggs could actually be fertilized, have shown that the size of the zinc sparks is a direct reflection of the egg's quality and ability to grow into a viable embryo.

In vitro game changer

Currently, during the in vitro fertilization (IVF) process, doctors don't know how viable a fertilized egg or embryo is until pregnancy occurs. But if scientists are able to develop a way to measure zinc sparks without harming the zygote, it could be a game changer.

"This means if you can look at the zinc spark at the time of fertilization, you will know immediately which eggs are the good ones to transfer in in vitro fertilization," Teresa Woodruff, one of the study's senior authors and a Northwestern University professor of obstetrics and gynecology, said in a news release.

Using only the most viable embryos could save a lot of time and heartache for IVF patients, while sparing them from the potential risks of extended embryo culture (keeping the embryo in a culture medium from the third day of fertilization on, which has been associated with pre-term births) and multiple embryo transfer (which increases the risk of becoming pregnant with multiple fetuses), the study says.

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