Embryos made without sperm or eggs reveal why many pregnancies fail

Embryo models closely resemble early human embryos Inside a lab in Vienna, cells are dividing to form a hollow sphere. Although the fragile ball has all the characteristics of an early human embryo, it isn’t quite what it seems. It didn’t, in fact, begin with an egg meeting a sperm.

Instead, it was created entirely in the lab. The very first days of pregnancy have long been an enigma. Scientists are unable to peer inside the uterus during pregnancy, meaning we know little about why so many fail. This is now beginning to change, thanks to embryo models created from stem cells, which are lifting the lid on one of the great mysteries of human biology. In the five years since early human embryo models known as blastoids were first created in several labs – including the one in Vienna – researchers have dramatically advanced our understanding of the early days of life. This is already leading to improvements for in vitro fertilisation (IVF) and treatments for serious conditions that occur during pregnancy. Blastoids are allowing scientists to recreate early pregnancy in a dish and then “poke it, perturb it and see how the system copes”, says Peter Rugg-Gunn , a developmental biologist at the University of Cambridge. As the science evolves and researchers are able to sustain embryo models in the lab for longer, they are beginning to find themselves in ethically uncharted territory. They’re faced with a quandary: just how far should they go? After an egg is fertilised, it begins dividing rapidly, forming a ball of cells that becomes a blastocyst. To keep developing, the blastocyst must dig into and attach to the uterus, which happens in humans around a week after fertilisation. This process, called implantation, often goes wrong.

Key points

• Instead, it was created entirely in the lab.
• The very first days of pregnancy have long been an enigma.
• Scientists are unable to peer inside the uterus during pregnancy, meaning we know little about why so many fail.
• This is now beginning to change, thanks to embryo models created from stem cells, which are lifting the lid on one of the great mysteries of human biology.
• In the five years since early human embryo models known as blastoids were first created in several labs – including the one in Vienna – researchers have dramatically advanced our understanding of t…