Pregnancy is a uniquely intimate relationship between two people. All of us luxuriate in this relationship once, and half of us are lucky enough to be able to do it all over again a second time. This tiny, greasy, pink baby that has just landed in our laps and looks as if it is trying to scream itself inside out - what sort of journey has brought it here? How are we able to make one of these amazing little people, who arise seemingly out of nothing? Written for the general reader, A Visitor Within reveals how pregnancy actually works. Why, for example, do women have a limited supply of eggs? How does an embryo halt its mothers menstrual cycle? How does a mother know she is pregnant? How is a baby put together? Why does the mother accept the foreign baby? How do mother and baby survive birth? Why are identical twins never actually identical? Why do women undergo the menopause? In charting our progress with these and other questions, David Bainbridge tells the story of a single pregnancy from conception to breastfeeding.