Gestation is the period during which an embryo or fetus develops inside the womb of a female mammal. This process begins after fertilization, when a sperm cell joins with an egg cell, forming a zygote. The length of gestation varies by species; for example, humans typically have a gestation period of about nine months, while elephants can be pregnant for nearly two years. During gestation, the developing organism undergoes significant growth and development. Nutrients and oxygen are supplied through the placenta, which connects the fetus to the mother's blood supply. This crucial stage ensures that the offspring are ready for survival outside the womb at birth.