Editing Menstrual cycle (section)

==Anovulatory cycles and short luteal phases==
{{Main|Anovulation}}
Only two-thirds of overtly normal menstrual cycles are ovulatory, that is, cycles in which ovulation occurs.{{sfn|Prior|2020|p=45}} The other third lack ovulation or have a short luteal phase (less than ten days<ref name = Liu>{{cite book |vauthors= Liu AY, Petit MA, Prior JC|chapter= Exercise and the Hypothalamus: Ovulatory Adaptations|date=2020|doi=10.1007/978-3-030-33376-8_8|title=Endocrinology of Physical Activity and Sport|pages=124–147|veditors=Hackney AC, Constantini NW|series= Contemporary Endocrinology|publisher=Springer International Publishing|isbn=978-3-030-33376-8|s2cid= 243129220}}</ref>) in which progesterone production is insufficient for normal physiology and fertility.{{sfn|Prior|2020|p=46}} Cycles in which ovulation does not occur ([[anovulation]]) are common in girls who have just begun menstruating and in women around menopause. During the first two years following menarche, ovulation is absent in around half of cycles. Five years after menarche, ovulation occurs in around 75% of cycles and this reaches 80% in the following years.<ref name="pmid29537383">{{cite journal |vauthors=Elmaoğulları S, Aycan Z |title=Abnormal uterine bleeding in adolescents |journal=Journal of Clinical Research in Pediatric Endocrinology |volume=10 |issue=3 |pages=191–197 |date=July 2018 |pmid=29537383 |pmc=6083466 |doi=10.4274/jcrpe.0014 }}</ref> Anovulatory cycles are often overtly identical to normally ovulatory cycles.{{sfn|Prior|2020|p=44}} Any alteration to balance of hormones can lead to anovulation. Stress, anxiety and [[eating disorder]]s can cause a fall in GnRH, and a disruption of the menstrual cycle. Chronic anovulation occurs in 6–15% of women during their reproductive years. Around menopause, hormone feedback dysregulation leads to anovulatory cycles. Although anovulation is not considered a disease, it can be a sign of an underlying condition such as [[polycystic ovary syndrome]].<ref>{{cite web
 |url=https://emedicine.medscape.com/article/253190-overview
 |title=Anovulation
 |vauthors=Hernandez-Rey, AE
 |date=August 2, 2018
 |website=Medscape
 |publisher=Medscape LLC
 |access-date=March 30, 2021
 |archive-date=20 March 2021
 |archive-url=https://web.archive.org/web/20210320153521/https://emedicine.medscape.com/article/253190-overview
 |url-status=live
 }}</ref> Anovulatory cycles or short luteal phases are normal when women are under stress or athletes increasing the intensity of training. These changes are reversible as the stressors decrease or, in the case of the athlete, as she adapts to the training.<ref name = Liu/>