The time between fertilization of an ovum and the birth of the young is called the gestation period. Humans have a gestation period of around 37 weeks or about 9 months and 1 week. Syrian hamsters have a gestation period of 16 days. That is believed to be the shortest gestation period for a mammal. The time the gestation period takes depends on the size of the animal, smaller ones have short lengths and bigger ones have the opposite.