oligoamenorrhea oligoamenorrhea oligoamenorrhea, also known as irregular infrequent periods or irregular infrequent menstrual bleeding, is a collective term to refer to both oligomenorrhea (infrequent periods) and amenorrhea (absence of periods). it is a menstrual disorder in which menstrual bleeding occurs on an infrequent and irregular basis. menstrual intervals are 37 to 180 days in oligoamenorrhea. nearly 90% of women with oligoamenorrhea have polycystic ovary syndrome (pcos). oligoamenorrheaother namesoligoamenorrhoea oligoamenorrhœa; irregular infrequent periods; irregular infrequent menstrual bleeding; irregular infrequent menstruation; oligomenorrhea/amenorrheaspecialtygynecology