Waiting for an elevated FSH--too late a marker of reduced ovarian reserve?

Aim: To assess age at which median follicle-stimulating hormone (FSH) is elevated above 10 U/L.

Background: Fertility and ovarian reserve decrease over the 4th decade with evidence that sensitive markers such as anti-Mullerian hormone fall even earlier. Despite its limitations, a basal or day 2-3 FSH is commonly used to assess ovarian reserve with levels over 10 U/L often used as a cut-point for further investigations.