The Modern Laboratory · Room 2 of 8

Room 2

One sperm, one egg

How a single sperm, placed gently inside an egg, brought hope to millions of couples.

For many couples, early IVF could not help. When a man's sperm were too few, or could not swim well enough to enter the egg, fertilisation in the dish simply did not happen. The answer, when it came, was beautifully direct: choose one sperm, and place it inside the egg.

The idea began with a hamster. In 1976, in Hawaii, Ryuzo Yanagimachi and his colleague Tsuyoshi Uehara injected sperm directly into hamster eggs, and watched them begin the first steps of fertilisation. It was the first proof that a sperm placed inside a mammalian egg could begin fertilisation. Yanagimachi already appears in this museum as the scientist who gave IVF its hamster workbench.

Then came Brussels. At the Centre for Reproductive Medicine of the Free University of Brussels, a team led by André Van Steirteghem and Paul Devroey was trying to help sperm across the egg's outer shell by placing them just beneath it, a method called SUZI. Sometimes a sperm went a little further, right into the egg itself. Gianpiero Palermo and his colleagues noticed that these eggs fertilised normally. So they began to do it on purpose.

On 4 July 1992 the team told the world in The Lancet: Palermo, Joris, Devroey and Van Steirteghem, “Pregnancies after intracytoplasmic injection of single spermatozoon into an oocyte.” From their first patients came two healthy boys and a pair of twins, a boy and a girl.

The skill in the hands. ICSI is a delicate act. Under the microscope, the embryologist holds the egg still with one fine glass pipette, gently stops a single sperm by touching its tail, draws it into a second, even finer needle, and slips it into the heart of the egg. It takes a minute, and years of practice.

From the bench

The first ICSI film on the internet, Oxford, about 1998

“I was working as an embryologist at the Oxford Fertility Unit, and the internet was still new. I took a video tape of ICSI to the emerging technology group at Oxford University, who were pioneering video on the web at the time, and asked them to digitise it. It took a long time to create a small video, but it was enough to show online, on the unit's website. It was later used in a BBC News story.

Sadly the video is lost to time, but the memories, and a screenshot, still remain.”

Thomas Elliott, embryologist, Oxford Fertility Unit

ICSI changed the story of male infertility. Men who had been told they could never be fathers now could. Today it is part of a large share of IVF treatments around the world, and millions of children have been born from it.

Denny Sakkas looked inside the sperm. A sperm cell can swim beautifully and still carry damaged DNA. Denny Sakkas, who studied at the University of Melbourne and earned his PhD at Monash University, working with Alan Trounson, has spent much of his career showing why that matters. At the University Hospital of Geneva in the 1990s, working closely with colleagues at the University of Modena in Italy, he studied how tightly the DNA inside each sperm head is packed. In 1996 he and his team found that for men whose sperm DNA was more often poorly packaged or broken, eggs that failed to fertilise after ICSI were more likely to hold a sperm that had never unpacked its DNA. He carried this work on at Birmingham Women's Hospital in England and then at Yale University School of Medicine, where he directed the IVF laboratories, and in 2004 he and his colleagues showed that the more sperm in a sample carried broken DNA, the fewer embryos went on to reach the blastocyst stage. His work helped the whole field see that a good sperm is more than a fast one. He is now Chief Scientific Officer at Boston IVF, and in 2025 he received the Distinguished Researcher Award of the American Society for Reproductive Medicine.