Anovulatory cycle
While the normal menstrual cycle in the human typically lasts 4 weeks (28 days, range 24–35 days) and consists of a follicular phase, ovulation, and a luteal phase, followed by either menstruation or pregnancy, the anovulatory cycle has cycle
lengths of varying degrees. In many circumstances, menstrual intervals are prolonged exceeding 35 days leading to oligomenorrhea (cycle >35 – 180 days interval), or even longer, amenorrhea. In other cases, menstruation may be fairly regular (eumenorrhea), or more frequent (intervals < 21 days), or there may be a loss of menstrual pattern (menorrhagia, dysfunctional uterine bleeding).
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.