When health begins

Fertilization produces a single-cell embryo prior to the onset of cell division. The number of cells in an adult is estimated to be between 30 trillion and 100 trillion. To reach these large numbers from a single cell, 46 to 47 generations of cells, to a first approximation, are required. Most cell generations appear before birth while most cells appear after birth. Therefore, it is perfectly reasonable to think that the quality of the prenatal environment in which the first 41 generations of cells develop before birth will influence the health of all the cells that develop after birth. Endowment for Human Development