Horizon explores the secrets of what makes a long, healthy and happy life. It turns out that a time you can't remember - the nine months you spend in the womb - could have more lasting effects on you today than your lifestyle or genes.
It is one of the most powerful and provocative new ideas in human science, and it was pioneered by a British scientist, Professor David Barker.
His theory has inspired a field of study that is revealing how our time in the womb could affect your health, personality, and even the lives of your children.
Watch the full documentary now