Bottlenose Dolphin - Mother giving birth to Baby / Calf (Tursiops truncatus). Birth Sequence 1. Part of a sequence of imagesDolphin gestation / pregnancy lasts approx. 12 months, the birth can take between half an hour to 3 - 4 hours depending on the experience of the mother. Weaned after 9 - 18 months. Young stay closely with mothers for up to 6 years.