What is Oligoovulation and Anovulation?
Anovulation is the complete absence of ovulation (egg release from the ovary), while oligoovulation refers to infrequent or irregular ovulation, both resulting in menstrual irregularities and potential infertility. 1
Physiological Context
Ovulation normally occurs during days 9-20 of an average 28-day menstrual cycle. 1 After ovulation, the ruptured follicle transforms into the corpus luteum, which produces progesterone to prepare the uterine lining for potential pregnancy. 2 When ovulation fails to occur or occurs irregularly, this normal hormonal cascade is disrupted.
Clinical Manifestations
Women with anovulation or oligoovulation typically present with:
- Amenorrhea (absence of menstruation) 3
- Oligomenorrhea (infrequent menstruation, typically cycles >35 days apart) 3
- Abnormal uterine bleeding (heavy, irregular bleeding patterns) 1, 3
- Infertility (inability to conceive despite regular unprotected intercourse) 4
Common Underlying Causes
Polycystic Ovary Syndrome (PCOS)
PCOS is the most common cause of chronic anovulation, affecting 4-10% of reproductive-aged women. 1, 5, 4 Women with PCOS experience hyperandrogenism, insulin resistance, and polycystic ovarian morphology (>25 small follicles per ovary or ovarian volume >10 mL on ultrasound). 1
Functional Hypothalamic Amenorrhea (FHA)
FHA results from chronic suppression of GnRH pulsatility due to stress, excessive exercise, energy deficit, or low body weight. 1, 5, 6 This leads to inappropriately low FSH and LH levels (typically <2-3 IU/L) despite low estrogen. 1, 6
Hyperprolactinemia
Elevated prolactin suppresses GnRH pulsatility at the hypothalamic level, causing anovulation. 6, 7 This accounts for approximately 20% of anovulatory cases. 7
Advanced Liver Disease
Women with advanced liver disease experience altered estrogen metabolism and disruption of the hypothalamic-pituitary axis, leading to anovulation and amenorrhea in more than 25% of cases. 1
Other Endocrine Disorders
- Thyroid dysfunction (both hypo- and hyperthyroidism) 1, 5
- Primary pituitary disease (adenomas, mass lesions) 1, 6
- Premature ovarian failure 1
- Hyperandrogenic conditions beyond PCOS 1
Physiological States
Anovulation is normal during puberty, the postpartum period (especially with breastfeeding), perimenopause, and pregnancy. 1, 8, 7
Diagnostic Confirmation
Mid-luteal phase serum progesterone ≥5 ng/mL (≥16 nmol/L), typically measured on day 21 of a 28-day cycle, confirms ovulation occurred. 2 Levels below this threshold suggest anovulation, mistimed sampling, or luteal phase defect. 2
Clinical Significance
Chronic anovulation increases the risk of endometrial hyperplasia and cancer due to unopposed estrogen exposure. 5 Women with anovulation who are not seeking pregnancy require cyclic progestin therapy or combined hormonal contraception to protect the endometrium. 1, 5
Anovulation represents a major cause of infertility, with ovulatory disorders accounting for approximately 21% of female infertility cases. 1, 4 However, even women with advanced liver disease or decompensated cirrhosis can occasionally ovulate, underscoring the need for contraception counseling when pregnancy is not desired. 1
Important Clinical Pitfall
The diagnostic challenge of distinguishing FHA with polycystic ovarian morphology (FHA-PCOM) from true PCOS is critical, as nearly half of women with FHA may have PCOM on ultrasound. 1, 5 Key distinguishing features include typical FHA triggers (excessive exercise, energy deficit, psychological stress), lower LH and testosterone levels, higher SHBG, and positive response to progestin challenge testing in FHA. 1