<Ul> <Li> WHO group I: Hypothalamic--pituitary - gonadal axis failure </Li> <Li> WHO group II: Hypothalamic--pituitary - gonadal axis dysfunction . WHO group II is the most common cause of ovulatory disorders, and the most common causative member is polycystic ovary syndrome (PCOS). </Li> <Li> WHO group III: Ovarian failure </Li> <Li> WHO group IV: Hyperprolactinemia </Li> </Ul> <Li> WHO group I: Hypothalamic--pituitary - gonadal axis failure </Li> <Li> WHO group II: Hypothalamic--pituitary - gonadal axis dysfunction . WHO group II is the most common cause of ovulatory disorders, and the most common causative member is polycystic ovary syndrome (PCOS). </Li> <Li> WHO group III: Ovarian failure </Li>

The male sperm and the female eggs the ova can be classified as