Physical growth begins when the egg and sperm combine.
The size and shape of a human results from the original genetic information or program. This is also true for growth during the time an individual is in the womb. Normal growth in the womb occurs at a very rapid rate. The average time in the womb is forty weeks and is called the gestational period. A premature baby is smaller but is usually AGA because the size is appropriate for the length of time the baby is in the womb.