Elephants have nearly a two year gestation period.
It would take a long time to be able to tell if an elephant is pregnant just by looking at her. Blood, collected on a weekly basis, allows the animal handlers to evaluate hormone progesterone levels. Serum progesterone rises after ovulation and in a non-conceptive cycle will then remain elevated for eight to ten weeks. If conception occurs, the progesterone levels will rise after ovulation and breeding, never returning to baseline during a normal pregnancy. It is a drug fact sheet about the drug aricept.