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).
Common torpedo
The common torpedo is aplacental viviparous, in which the embryos are sustained by yolk, supplemented by histotroph ("uterine milk") secreted by the mother. However, the organic content of the histotroph in this species is only 1.2%, much lower than in stingrays, and the embryo loses mass over the course of development as its initial yolk supply is expended for metabolic processes. Adult females have two functional ovaries and two functional uteruses, though the reproductive tract on the right side is more developed and consequently tends to carry more embryos. It has an annual reproductive cycle with well-defined seasonality, though the details differ between geographic regions. In the Mediterranean, mating occurs from December to February and birthing from late August to early September after a gestation period of 4–6 months; litter sizes range up to 19 and the newborns measure long. By contrast, off West Africa the gestation period lasts 6–8 months and birthing occurs from September to October; litter sizes range up to 28 and the newborns measure long. The litter size increases with female size.