See the First 3D Images of a Human Embryo Implanting, Shedding Light on the Crucial but Little-Known Process

A new study shows how human embryos reshape their environment by pulling on uterine tissue

August 19, 2025

A human embryo embedding itself into the fake uterus. — A human embryo embeds itself into a fake uterus created by researchers. Screenshot from an Institute for Bioengineering of Catalonia video

Sixty percent of miscarriages are caused by the failure of an embryo—the developmental stage before a fetus—to implant in the woman’s uterus. Part of the problem is that researchers have no idea how an embryo implants itself in the uterus to begin with—in other words, exactly what needs to go right and what could go wrong remain largely a mystery.

Now, however, a team of researchers has taken a giant step forward in understanding fertility by capturing the first real-time and 3D images of a human embryo implanting into uterine-like tissue. Together, the snapshots look like a stop-motion film. Before this study, published Friday in the journal Science Advances, researchers had only observed still images from particular moments during implantation.

The process is “very inaccessible, because it’s all happening inside the mother,” Samuel Ojosnegros, senior author of the study and a bioengineer at the Institute for Bioengineering of Catalonia in Spain, tells Nature’s Jenna Ahart. “It’s such an important process for human reproduction, but at the same time, we don’t have the technology to study it.”

Need to know: What is an embryo?

An embryo describes the stage of development between the fifth and tenth weeks of pregnancy, during which cells multiply and important organs begin to form.

Ojosnegros and his colleagues created a makeshift uterus with a lining made from a collagen-rich gel. This simulated the natural matrix—the scaffolding that holds our cells together—found in uterine tissue, which contains collagen and other proteins. They then recorded how human embryos, donated via a local hospital, interacted with the substance by using a microscope to snap a picture every 20 minutes for 16 to 24 hours, reports Nature.

“We can see how the embryo penetrates this matrix and sort of digs a hole in the matrix. It’s very, very beautiful. And it’s very, very surprising, because we knew that the embryo had to do something like that, but it had never been recorded how they do it,” Ojosnegros tells NPR’s Rob Stein. “It’s quite stunning to see it live.”

Embryos burrow into the uterus with significant force, release enzymes to break down the uterine tissue and form specialized tissues to connect with the organ’s blood vessels to start feeding, Ojosnegros explains in a statement. He says that it is “a surprisingly invasive process” during which many women bleed and feel abdominal pain.

What his team revealed, however, is how the embryos reshaped their environment within the uterine tissue by pulling on the synthetic matrix. What’s more, when the researchers applied external force to the matrix with forceps, the embryos reacted by moving toward the impacted areas. “We believe these micro-contractions are what the embryo uses to guide itself toward the blood vessels and the nutrients it needs,” Ojosnegros says to Scientific American’s Humberto Basilio, while adding that further research is necessary to build confidence in that idea.

The researchers also observed the implantation of mouse embryos and noted that they adhere to the surface of the uterus, which then envelopes the embryo. This is markedly different from human embryos, which force their way completely into the tissue. The team also found that, for both mice and humans, the embryos that exerted more force on the uterine lining were more likely to implant, per Scientific American.

Norbert Gleicher, an infertility specialist at New York’s Center for Human Reproduction who was not involved in the study, tells Forbes’ Leslie Katz that the images are an “important first observation,” adding, however, that they only highlight one aspect of what dictates an implantation’s success. Implantation is “a mechanical process, but at least in my opinion, it is first and foremost an immunological process.”

Nevertheless, Magdalena Zernicka-Goetz, a biologist at the California Institute of Technology who was also not involved in the study, tells NPR, “I’m very excited to see this study,” and that “it really takes a major step toward opening one of the black boxes of human development. It’s beautiful.”

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