The gestation period of a blue whale (Balaenoptera musculus), which is the largest known animal on Earth, is estimated to be around 10 to 12 months. During this period, the female blue whale carries the developing fetus inside her womb. After the gestation period, she gives birth to a single calf, which is already a significant size at birth, measuring around 23 to 27 feet (7 to 8 meters) in length and weighing several tons. The extended gestation period of the blue whale is necessary for the growth and development of such a massive species.