Ovulation disorders, presenting as menstrual disturbance, are the cause of infertility in around 25% of couples who have difficulty conceiving. The World Health Organization (WHO) categorizes ovulation disorders into three groups:
Group I ovulation disorders (hypogonadotropic hypogonadal anovulation) are caused by the hypothalamic pituitary failure. This category includes conditions such as hypothalamic amenorrhea and hypogonadotropic hypogonadism. Typically, women present with amenorrhoea (primary or secondary) which is characterized by low gonadotrophins and estrogen deficiency. Approximately 10% of women with ovulation disorders have a group I ovulation disorder.
“Women in group I typically present with amenorrhea and low gonadotropin levels, most commonly from low body weight or excessive exercise.” AAFP (2015)
Group II ovulation disorders (normo-gonadotropic, normo-estrogenic anovulation) are defined as dysfunctions of the hypothalamic-pituitary-ovarian axis. This category includes conditions such as polycystic ovary syndrome and hyperprolactinemic amenorrhoea. Around 85% of women with ovulation disorders have a group II ovulation disorder.
Group III ovulation disorders (hyper-gonadotropic, hypoestrogenic anovulation) are caused by ovarian failure. Around 5% of women with ovulation disorders have a group III ovulation disorder.
Reference
https://www.ncbi.nlm.nih.gov/books/NBK327781/ Accessed 8/12/2017