Imagine being able to observe with astonishing clarity a child's delicate features as they evolve over the course of a pregnancy, or witness the complex behavior of new human life in utero. Now we can, thanks to the advent of innovative 3D and 4D imaging technologies that provide a powerful diagnostic tool for doctors and cast vivid light on our earliest development-and a profound new way for parents to bond with their babies on a deeper emotional level. Each spread features a central image and information about that particular stage as well as brief commentary explaining what we know and how we know it. For example, at 24 weeks we watch a fetus open and close her eyes, display facial expressions resembling a grimace and a frown, and stick out her tongue (no one has yet established exactly why). And during the last trimester, we learn, she experiences REM sleep and can hear loud noises through the fluids of her mother's body-a first hint of the world that awaits outside the womb.