The Modern Laboratory · Room 8 of 8

Room 8

Watching it grow

The scientists who learned to film an embryo's first days, and what those quiet films have taught us.

For most of IVF's history, an embryologist saw an embryo only in snapshots. Once or twice a day the dish was lifted from the warm incubator, checked under the microscope, and put back. Everything that happened in between, every division and every small hesitation, went unseen. Our embryo has been luckier. A small camera has watched over it from the very beginning, taking a picture every few minutes, so that its whole life so far can be played back like a film.

The first films. In Adelaide, at the University of Adelaide's Reproductive Medicine Unit at The Queen Elizabeth Hospital, Payne, Flaherty, Barry and Matthews used time-lapse video to follow 50 human eggs through the hours after ICSI. Published in Human Reproduction in 1997, their study revealed fertilisation as a sequence of living events: gentle waves rippling through the egg's cytoplasm, the second polar body appearing, and the two pronuclei forming and drawing together until they touched. In Japan, Mio and Maeda filmed embryos from fertilisation right through to hatching, and in 2008 described watching identical twins begin to form from blastocysts growing in the dish.

Timing tells a story. At Stanford University, Connie Wong, Renee Reijo Pera and their colleagues combined time-lapse imaging with studies of gene activity. In Nature Biotechnology in 2010 they reported that three simple timings, all measurable by the second day, could predict which embryos would go on to reach the blastocyst stage. Much of an embryo's future, it seemed, was already being written in its first few divisions.

From watching to choosing. In Valencia, Marcos Meseguer and his colleagues followed hundreds of embryos, photographed every 15 minutes, whose implantation was then known. In Human Reproduction in 2011 they identified timings linked to implantation, such as when an embryo reached five cells, and proposed a model to rank embryos by their chances. The word “morphokinetics”, the study of shape and timing together, entered the everyday language of the laboratory.

Careful questions from Aarhus. At Aarhus University Hospital in Denmark, Kirstine Kirkegaard and her colleagues asked the questions every new technique deserves. In a randomised trial published in 2012 they showed that embryos developed just as well in a time-lapse incubator as in a conventional one. In 2013 they found that early timings could predict which embryos would become good blastocysts, but not which would lead to pregnancy, and suggested that one universal timetable for every embryo might not exist.

What the large trial found. The TILT trial, published in The Lancet in 2024, enrolled 1,575 people at seven clinics in the United Kingdom and Hong Kong. Live birth rates were similar whether embryos were cultured and chosen with time-lapse, cultured undisturbed with time-lapse alone, or cared for in the standard way. Time-lapse does not promise more babies. Its gifts are gentler: calm, uninterrupted culture, a far richer understanding of how life begins, and a complete record of every embryo's first days. Today, computer programs are also being studied to help read these films.

And so our embryo's journey through the laboratory is complete. It began as an egg and a sperm, and now it is a blastocyst, ready to go home to its parents, with the whole story of its first days kept safe on film. Every one of the people in these rooms helped it on its way. In 1978, Louise Brown began her life with no camera watching at all. Since then, millions of families have followed the path she opened.