Why are we the way we are? Why is it that for some people, standing up and speaking to a bunch of strangers in a pub is like water off a ducks back, while for others the thought of it sends them running for the hills? Why are some of us prone to being anxious, depressed or fat? Nature, nurture and our lifestyle influence how we develop. However, there’s another important factor that can shape who we are ─the 9 months we spend in the womb. I will describe how the environment we encounter in the womb, can influence our behaviour, intelligence, appetite and our susceptibility to develop disease.