The Modern Laboratory · Room 3 of 8

Room 3

Growing in the dish

A teacher and his student, and how they learned what a young embryo needs to thrive.

An embryo is not the same creature on day one as it is on day five. In its first days it lives quietly on simple fuels; by the time it becomes a blastocyst it is busy and hungry, like a growing child. For years IVF laboratories fed embryos the same broth all the way through, and many never reached day five. The answer came from asking a beautifully simple question: what does an embryo actually eat?

Henry Leese listened to embryos. At the University of York, where he worked from 1969, Henry Leese devised gentle ways to measure what a single living embryo takes in and gives out, without harming it, using tiny droplets of fluid around each embryo. He studied the fluid of the oviduct, the embryo's first natural home, to learn what nature provides. In 2002 he proposed the “quiet embryo” idea: that the healthiest embryos are often the calmest, using just the energy they need, an idea scientists still explore today. He was awarded the Marshall Medal of the Society for Reproduction and Fertility in 2010 and served as President of the British Fertility Society from 2015 to 2018.

Then came his student. In 1984 a young PhD student named David Gardner arrived in Leese's laboratory. Their 1986 paper, measuring the nutrients taken up by single mouse embryos, appeared in the very first issue of Human Reproduction.

David Gardner fed embryos what nature does. From York he went to John Biggers at Harvard, whom you may already have met in The Animal Work, and then to Alan Trounson at Monash. Studying the fluids of the oviduct and the uterus, he and his colleague Michelle Lane designed culture in two steps: one medium for the early embryo, and a second for the days that follow, as the embryo's needs change. These became known as sequential media.

In 1997 Gardner joined William Schoolcraft at the Colorado Center for Reproductive Medicine in Denver. There they showed that growing embryos to the blastocyst stage and transferring them on day five raised the chance of each embryo implanting, and so reduced the need to transfer several embryos at once. Together they also created a simple way to describe a blastocyst with a number and two letters, such as “4AA”. It is still the most widely used grading system in the world, and many patients will recognise it from their own embryo reports.

He later became Head of Zoology at the University of Melbourne, and in 2017 was elected a Fellow of the Australian Academy of Science. Teacher and student, between them, changed what it means for an embryo to grow in a dish.