Clinical meaning
Infertility is defined as the inability to conceive after 12 months of regular unprotected intercourse (6 months if female partner is ≥35 years). The process of conception requires coordinated function across multiple systems: hypothalamic GnRH pulsatility driving pituitary gonadotropin secretion, ovarian folliculogenesis and ovulation, tubal patency for oocyte-sperm interaction, adequate sperm production and function, and a receptive endometrium for implantation.
At the molecular level, ovarian reserve reflects the remaining pool of primordial follicles established during fetal life. Each menstrual cycle, a cohort of follicles is recruited by rising FSH, but only the dominant follicle (with the highest FSH receptor density and lowest FSH threshold) survives selection while others undergo atresia via Fas/FasL-mediated apoptosis. Anti-mullerian hormone (AMH), produced by granulosa cells of pre-antral and small antral follicles, serves as the primary biomarker of ovarian reserve - it reflects the recruitable follicle pool independent of cycle day.
Ovulatory dysfunction (WHO classification) accounts for approximately 25-30% of female infertility. Class I (hypogonadotropic hypogonadism) results from hypothalamic or pituitary failure - inadequate GnRH pulsatility from functional hypothalamic amenorrhea (energy deficit, stress), pituitary tumors, or Sheehan syndrome. Class II (normogonadotropic - most commonly PCOS) involves follicular arrest due to hyperandrogenism and insulin resistance disrupting FSH-dependent follicle selection. Class III (hypergonadotropic) reflects premature ovarian insufficiency (POI) with accelerated follicle depletion.
Tubal factor infertility (25-35%) most commonly results from Chlamydia trachomatis or Neisseria gonorrhoeae-induced salpingitis causing epithelial damage, deciliation, and peritubal adhesions. The inflammatory cascade activates toll-like receptors (TLR2, TLR4) on tubal epithelial cells, triggering NF-kB-mediated cytokine release (IL-1, IL-6, TNF-α), leading to fibroblast activation and tubal fibrosis/occlusion.