Treating Infertility: Making Babies

Couched in a halo of nutrient cells, an egg smaller than the dot on an i drifts slowly down a Fallopian tube, one of a pair of narrow passages that lead from a woman's ovaries to her womb. Like a beacon guiding ships at night, the egg sends forth a calling signal. A convoy of sperm -- the remnants of an armada that was once a couple of hundred million strong -- sails into view, their long tails thrashing vigorously. Lured by the chemical signal, several hundred of the most energetic swimmers close in on the egg, their narrow tips unleashing...