Menstruation
Menstruation is the most visible phase of the menstrual cycle and its beginning is used as the marker between cycles. The first day of menstrual bleeding is the date used for the last menstrual period (LMP). The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults (an average of 28 days).
Short-beaked common dolphin
Similar to humans, the short-beaked common dolphin is viviparous. Though they have the ability to carry twins, triplets, etc., they usually only carry one baby at a time. The Short-beaked common dolphin has a gestation period of 10 to 11 months. The newborn calf has a length of between and weighs about . For the Black Sea population, weaning occurs at between 5 and 6 months, but occurs later (up to about 19 months) in other areas. Typical interbirth interval ranges from 1 year for the Black Sea population to 3 years for eastern Pacific Ocean populations. Age of sexual maturity also varies by location, but can range between 2 and 7 years for females and 3 and 12 years for males. Common short-beaked dolphins have been observed to engage in oral sex, intimating that they – like chimpanzees and humans – engage in sexual activities for pleasure.