Many studies demonstrated that an elevated level of basal FSH affects both ovarian quality and quantity. Elevated basal FSH levels are indicative of diminished ovarian reserve (capacity of the ovary to provide egg) and women with higher basal FSH levels have frequently decreased oocytes retrieved in IVF program. The determination of ovarian reserve by measuring day 3 basal FSH among normal cycling women is one of the most commonly used tests for predicting success in IVF treatment.
Several studies have reported that women with an elevated FSH level have poor response to ovarian stimulation that leads to a lower pregnancy rate in ART regardless their age. However, other authors argued that young age does not protect against the adverse effects of reduced ovarian reserve. They also suggest that an elevated basal FSH is associated with poor quality oocytes leading to reduction in pregnancy rate and in miscarriage rates.
Elevated FSH levels have been shown to be associated with damage to the germinal epithelium of the seminiferous tubule that are located within the testes. Plasma FSH levels usually correlate inversely with process of producing sperm (spermatogenesis), and therefore FSH is considered to be a clinically useful endocrine marker (hormonal sign) in the evaluation of infertile men.
There is a consensus that men with azoospermia (no sperm in semen) and testicular atrophy with significantly elevated FSH levels should undergo testicular biopsy if in vitro fertilization with intracytoplasmic sperm injection (ICSI) is an acceptable approach for both partners.