What initial investigations should I perform to confirm a diagnosis of Premature Ovarian Insufficiency in a woman under 40 presenting with amenorrhea?

To confirm a diagnosis of Premature Ovarian Insufficiency (POI) in a woman under 40 presenting with amenorrhea, the initial investigations should include:

• Clinical history assessment including menstrual pattern changes, previous medical or surgical treatments, and family history.
• Measurement of follicle-stimulating hormone (FSH) levels on two separate blood samples taken 4 to 6 weeks apart, showing elevated FSH levels consistent with ovarian insufficiency.
• Assessment of menopause-associated symptoms such as no or infrequent periods, taking into account whether the woman has had a hysterectomy.
• Do not rely on a single FSH test for diagnosis; two elevated readings are required.
• Anti-Müllerian hormone (AMH) testing is not routinely recommended for diagnosing POI.

These investigations help differentiate POI from other causes of amenorrhea and guide appropriate referral and management.